Does this mean that Arcane Blast now only increases the damage of Arcane blast, and not of all Arcane spells?

no, I think he is just reiterating how arcane blast already works (arcane blasts costs more, buffs damage of all spells).

Edit: Actually I'm wrong, looking at the tooltip on mmo champion the damage component does only effect arcane blast.

Primary Goal
Interesting gameplay centering around mana management

Basic Idea
Mana Adept increases damage at high mana
High damage spells consume lots of mana

Resulting Player Task
Casting high damage spells while maintaining high amounts of mana
and / or
countering burn out periods with quick mana regeneration

Design Tasks
Create different ways to manage mana, all are valid in different situations.
Offer different choices of mana management with a clear winner in most cases.
Best choice has to be clearly seen in game, no need of spreadsheets
Good results will be achievable by getting the feeling of the class and understanding it's mechanics, no need of spreadsheets
Best theoretical rotation will likely be theorycrafted, however will not be applicable in most cases due to encounter design and other variables that can not be factored in

Tools
Assuiming no big chunks of implementation time are available until cataclysm a basic toolset has to be used.
Adapting mechanic of mana adept
Balancing through calculations
Buffs / Debuffs
Existing Spellset
Existing UI

Prerequesits

• A mana reg rotation is available even at the expansions haste cap (the maximum haste value players presumably are able to achieve in Cata).
  The rotation would be something like:
  AB -> ABarr -> AB
  -> AM (if procced) -> start again
  or
  -> ABarr (if cooldown is lowered) -> start again
  or
  -> AB (if still sufficient as mana reg rotation) -> ABarr -> start again
  or
  -> Offschool spell (if none of the above applies) -> ABarr -> start again
• Mana reg scales with haste in a way that haste doesn't lower your performance due to higher mana consume with faster spells (not sure if this is the case right now, if not it should be implemented for Arcane anyways)

Existing mana regeneration tools
Evocation: Counters high damage rotation with cooldown use
Mana reg rotation

Suggestions

Adapting Mana Adept damage buff
Mana adept has clear thresholds for a behavior change (instead of applying a linear buff, though I'm not sure how it is implemented atm.). The numbers could look like:

• At 80% mana no increase or decrease is applied
• Below 80% mana a hyperbolic function is applied, that reduces the damage to 20% at 0 mana.
• Above 80% mana a function is applied, that increases the damage and scales with mastery rating.

Accomplished: The player has a relatively good idea on when man adept works in his favour and when it doesn't

Mana adept damage decrease timer
Mana adepts damage malus has a timer to only apply after a distinct period of mana consume, non mana regeneration or after casting x damaging spells. In addition if it is active it expires after a distinct percent of mana regenerated.
This could be implemented by debuffs: If you drop below 80% mana (or whatever the balanced threshold is) the debuff "Mana Junki" is applied. This debuff stacks up to 5 times and gets a stack each time you cast a damaging spell. After reaching 5 stacks it applies the damage decrease. After x% mana regenerated the debuff expires and the game starts again if you are still below 80%.
Variables to play around with

• Damage could be decreased from the beginning but only with a 20% per stack value to further smooth out damage decrease.
• Instead of letting the debuff expire on x% mana regenerated, the stack size could be reduced by x/5% mana regenerated. Then the stack should either not increase with spellcasts if you have a positive mana balance or should increase with y% mana consumed rather then per spellcast.

Accomplished: The possibility to even cast below 80% mana with clever use of burn - reg cycles. Below 80% "burn - reg" may be a more valid tactic then balanced mana use (I somewhat have a vision of starting with a balanced but still mana decreasing rotation at 100%, while going to higher damage rotations over run to 80% and falling into burn - reg cycles afterwards). The implementation via debuffs gives the player a clear feedback of the current situation.

Mana exhaustion
Further going the way of Mana Junki, the debuff could stack even higher (say to 10 stacks) and after reaching a stack size of 10 it transforms into the mana exhaustion debuff. Under influence of this debuff all spells stop damaging but reward mana in different ways: Arcane Barrage applies a MOT (Mana over time), Arcane Blast increases the effect of all mana regenerating spells cast on the target Arcane Missiles transforms it's damage to mana (in a valid ratio) and Arcane Explosion rewards an amount of mana from each target hit. All cooldowns and cast times are set to 0 for the duration of the buff (to shorten the regeneration period).
The debuff wears off at 100% mana, after a given time or maybe after a given amount of mana regenerated (or all of them). Maybe even after a given amount of targets hit under the debuff effect to give further choices on what reg strategie would be the best.
Maybe another spell (frost bolt?) would have to be taken into consideration too as a single target direct mana source if AM hasn't procced and for leveling (as AB comes fairly late) if Mana Adept is granted at level 10.
Accomplished: To reach the Arcane Exhaustion debuff may be a long way (Maybe 10 stacks are not enough) with low damage, but should reward the player with massive mana regeneration over a short period of time. The player has to choose whether to try to get the debuff at all and if so when the best time would be. The high damage rotation abilities coming off cool down may be a valid use to boost mana up to 100% before hands with this. Again the debuff gives a clear feedback.

Balancing concerns

• Raid replenishment effects
• The rotations, the mana adept impact and regeneration should be balanced to get the following as general strategie over the course of a long fight:
  • 100% Mana: either heavy damage rotation followed by Evocation or balanced but still mana consuming rotation (for example 3xAB->ABarr->2xAB->ABarr)
  • running towards 80%: rotations get heavier (as damage decreases, spells have to pull the weight)
  • below 80%: spiraling downwards (mana wise) with burn - reg cycles or regenerating upwards to start again with balanced rotations
  • nearing 0%: burning mana followed by heavy regeneration through Mana Exhaustion

Additional wishes
Fancy UI to represent all of this in a better way then buffs / debuffs can (at least the new inbuild Power Auras could be handy here).

Ingame explanation of effects
The arcane mages have mastered the direct manipulation of time and space. They extract the energies surrounding them from their environment, focus them and hurl them against their enemies to attack the very base of their existence, the space they ocupie, the time they exist in. But sipping at these energies of the world comes at a price. As the powers founding the world pulse through your body charging at blazing speed at your foes, they take little pieces of your own reality with them. Thus comes the time many mages sit down to rest and refresh them selfes, but the most skilled of the arcane masters have even mastered the ability to recapture the forces they threw at their enemies just moments ago and restore them selfes in the blink of an eye.

Regarding the new Arcane changes:

The Good:

1. Arcane gets a burn cycle again. Yes, in WotLK spamming AB is still ever so slightly a dps increase over ABx4, Missile Barrage, but it was never enough to be a burn cycle. Under this model spamming Arcane Blast will be a true burn cycle in that it will do substantially more dps than our normal cycle. If the glyph stays (and it has so far) a mage spamming Arcane Blast will be doing +92% damage.

2. Arcane AoE is that bit more useful and competitive. Pulling threat seems like a complete non-issue and though there is still the threat of cleaves etc, they never stopped me spamming AE in WotLK, which was very competitive under cooldowns, not so without.


The Bad:

1. Arcane Barrage and Arcane Missiles will hit like a wet lettuce. For Fire and Frost their proc and cooldown spells are big hitters (ie Pyroblast / Deep Freeze) that you're excited to cast. Missile Barrage was exciting to cast in WotLK. Rounding off your rotation with Arcane Barrage / Missiles is going to feel like a disappointment under this model. It will also have the effect of further weakening Arcane's ability to move - an Arcane Barrage without an stack bonus isn't going to cut it as our movement option.

2. The mana tools still aren't there to support Mana Adept. Having a burn cycle is great. Without the tools to support it, though, there can be no burn cycle. There's also the complication of when a burn cycle stops being worth it because the Mana Adept mastery counteracts the stack bonus as you drop mana.

3. Torment the Weak. A universally hated talent. Dropping this and replacing it with an active mana tool seems like a good idea.

While I may be wrong, it seems to me that with the current state of arcane mages that if in a vacuum 1% haste, 1% crit, and 1% mastery all gave the same dps increase (which is impossible even if that was the goal but serves a purpose to demonstrate...) that you would essentially want to avoid haste like the plague.

Given all things equal, haste comes with the downside of making you spend your mana faster. While it has often been easy to simply not care about this, or to just be slightly more aware of your casting to control when you go OOM, with Mana Adept this consequence affects every single cast you ever make. By spending your mana faster to do the same amount of damage as simply critting more often, you are giving up damage through the mastery.

Unless I'm mistaken it would seem to me as if the optimal amount of arcane mage haste is essentially zero, assuming that you could always trade it for equally budgeted amounts of crit and mastery (much like the ICC loot arrangement). In fact if it were possible to gear for negative haste and trade it for crit to a point where a AB*2 Abarr rotation became reliable that would possibly be the correct play.

Obviously this does not make haste by itself bad, but if X budget of haste and X budget of crit give the same theoretical dps increase, crit seems like it should be winning by a mile.
Just seems like an interesting and perhaps unintended departure from mage play in the past.