My guess is that we will be forced to use tier sets, mana reduction relics and their "class trinkets" just to reach some level of sustainability with this change instead of having free gear choice. It's the Earthfury story all over again and I don't like it at all. -.-#
This is even worse due to the fact that we still get only one tier 4 pants/chest per week - what's up with that anyway? [/rant]
Edit: To illustrate my point a little better...
http://www.wowhead.com/?item=30663 - Fathom-Brooch of the Tidewalker was deemed unnecessary because Elemental Focus would provide us with sufficient mana. This change kills our sustainability, making this trinket very desirable.
http://www.wowhead.com/?item=29389 - Totem of the Pulsing Earth was changed to a reduction of 24mp on test servers. That is still diminished by talents, giving an effective reduction of 22mp after Convection. While currently deemed trash, the efficiency boost will become highly desirable after the change.
http://www.wowhead.com/?spell=37237 and
http://www.wowhead.com/?spell=37237 - The 4-piece bonuses of our tiered epic sets all give sustainability bonuses. The big downside is that we get forced to keep a worse piece just for the set bonus and pick up higher tier loot for the bank till we reach 4 parts.
So in conclusion, instead of making our itemization more desirable in proper ways, they force us to take it just to be able to function at all. That balances things out for progressing raiders but leaves people without weekly access to tier 5 instances behind. This also makes sure that people with arena gear will not be able to function in a raid environment.
