Well Nilihum has offically cleared Hyjal and Black Temple now, and I'm sure Curse and others will be soon to follow.

The real question is, how long will it take the average guild to catch up to mid/end BT/Hyjal before they release the next set of raid content?

I'd say we're probably a few months off from anything new.

Zul'Aman will be a 10-Player zone like Karazhan, so there is no 25 content in the near future.

Exactly, in Nax this was true for the very first time. You could NOT lose anyone on Thaddius, every time we lost 2-3 DPS during the fight, we hit enrage and wiped.
You couldn't lose people on Gluth either, at least as Alliance. Once Gluth feeds, you're in trouble. Losing some of the very few DPS players your raid could afford on 4H was a guaranteed timeout wipe, losing a tank a disaster.
We've also never killed Gothik when anyone died before he came down.
In BWL this was not true, you could pull at least a dozen slackers through the raid, on C'Thun 5 people could eat death ray and you'd still win.

Using C'thun as an example is a poor choice for AQ40. Use Twin Emps instead, in pre-TE gear, and don't stack the raid.

And also consider Huhuran, a fight where the dps requirements meant losing people really really hurt.

Huhu & Twin Emps introduced the "ideas" of raiding that Blizzard continues to use.

-> Enrage timer where the boss goes ape-shit and starts nuking the raid with <ability X> that you can *deal* with ... for a limited time.
-> Enrage timer where you know the boss is going to 1-shot your tank, and you must kill him before it happens.

Twin Emps -> Gluth/Thaddius/Faerlina
Huhuran -> Maexxna/Loatheb

Moving into TBC raids:

Twin Emps -> Magtheridon (forgiving, but it's there)/Hydross
Huhuran -> Gruul/Morogrim (sorta)

I'd like to see some new mechanics, and the complete removal of the enrage timer. While this does allow for "cheese", it removes the entirely artificial "oh, you've been here for 10 minutes, I'm late for tea - OMG WHUP ASS" effect that makes no sense whatsoever.

Yes, but there are better ways to do it that don't feel so nakedly mechanical. Nefarian phase 1, for example - you have to have enough DPS and coordination to kill adds fast enough that you don't get overrun. Same with Magtheridon phase 1, or so I hear (not been there myself, probably never will). Any boss with healing abilities where you have to outdamage the healing. And so on.

Heck, even soft enrages (boss hits harder sub 20%, say) feel more "natural", and can provide just as stringent a DPS check. Or you can invert it, and have a raid-wide buff that wears off, like Essence of the Red. It makes organic sense - Vael gave the last of his power while sane to buff us as much as he could, but that was all he had left.

All the above are preferable to a hard enrage (timer hits 10 minutes and everybody dies). You just end up feeling "If $boss can kill us all without trying, why the heck doesn't he do it at the start of the fight".

If you want a hard enrage, there could be ways to do it - when you engage the boss, he sends a signal to summon his armies from the barracks. At 5 mins, you get yells that the reinforcements are on their way. At 8 minutes, you get the army commander yelling at the troops to buff up and get ready. At 10 minutes, you get zerged by 100 adds. If you kill him in time, you hear a yell telling the army to fall back to their next line of defence (and presumably these then form the trash mobs en route to the next boss).

TK instances would be the perfect place for this - it makes sense that Botanica would have some kind of inbuilt sterilisation system to cleanse it in case of infestation by dangerous organisms. So when you engage Warp Splinter, you get system messages to say something like "Failure of primary containment seal detected", followed by various status messages over the next couple of minutes, and finally the area gets flooded with poison gas after 5 minutes. Pathaleon could activate some kind of self-destruct on the Mechanar to prevent us getting our hands on the ship's weapon systems, and so on.

I'm only using these as examples because that's the instances I'm doing. I'm sure witha little thought you can find ways of applying the concept to raid bosses too. I don't know if there's a hard enrage timer on Magtheridon, but you could for example say that the boxes are damaged and run out of power after 10 minutes. There's yoru enrage timer, in a way that makes sense.

In summary - Timers: OK in moderation. Bosses suddenly wiping you when they've been fighting you for 10 minutes without using their uber powers: makes no sense.

The DPS check should more be focused on the inividual DPS'er though. Its quite annoying currently how the game place very strict gear requirements on tanks, who also usually need to farm for resist gear and such, while other classes get away with much less work.

Ideas would be trash/bosses with:

Back clash damage: Everytime someone does damage the mob does 4k Fire damage to the attacker. Possibly enough to force a major grind effort so anyone who wants to DPS the mob better have 350 resist. Well other option is to stop forcing resist checks on tanks but if there is a Resist check at all its very unfair to only require that some members of the raid grind for the stuff.

Vampiric regen: When a player does damage to a mob, said mob gains a buff that grants for instance +350 health/second and lasts 60 seconds. Stacks for different players and refresh when additional damage is dealt. Would be a nice mechanic to force individual DPS'ers to meet a minimum; or be totally useless for an encounter. Just like tanks have to meet a minimum gear check or they are totally useless.

Think its needed to have mechanics that make the gear checks more equal anyway.

So Essence of Souls then?

Forcing healers in pure healing equipment to DPS is hardly an acceptable solution though. They had to build in holy / nature weaknesses to work around that. What they could do is porting pure DPS (hunter WL mage rogue) classes to seperate rooms like Scholo GM did where they'd have to kill something within a time limit.

Once you've attuned everyone to SSC, there really is no need to go Nightbane apart from the loot. But hey, we've been doing it for the loot with alts now for a while

The question about bosses being optional or not really depends on why you're going to an instance. The final boss would be malchezaar, dropping the highest loot and such. If that's your goal, almost all bosses there are optional

However, if your goal is equipping your raid, there's not a single optional boss in the entire instance unless you really don't need a single drop from it.

He did say "unless you don't need a single drop from it," which is likely the reason no one does the animal boss. :P