So, as far as I know they want to somewhat keep the raidwide buff like they have in Icecrown Citadel now in Cataclysm aswell. So I came up with somewhat of an idea to not make it "ruin" the content.
Note: This is just an idea! No need to fla..nevermind! I'm not even gnna bother!
So the idea is, taking WotLK as an example, to increase the buff with 10% every time a new raid instance comes out with a content patch to a maximum of 10%.
Naxxramas was the first raid (ignoring OS and EoE). At first this raid will have 0% buff. Then in the next content patch Ulduar came out, the buff in Naxxramas will be increased to 10% in this patch and Ulduar will be at 0%. The patch after Ulduar, ToC came out, so the buff in Naxxramas will be increased to 20% and the one in Ulduar to 10%. Then Icecrown Citadel comes out, and well, I guess you understood the system now and you can figure out yourself what the buffs will be.
Lemme know what you think of this idea, this won't ruin content like it did in Icecrown Citadel right now (that's how I see it atleast, it just became to easy) but will still give the new players a boost to go through the content without to much trouble and keep up with the end game raiders eventually.
// Phine