Removing attunements will HELP the guilds currently working on SSC / TK by allowing them access to T6 loot.
No, in my opinion, it won't. This is because gear is relatively unimportant in raiding in TBC. The natural progression of raiding prepares the guild gear-wise for the boss they are working on. By the time a raid reaches a given boss, the raid will have enough gear to tackle the boss. The only guilds who are undergeared for the content they are working on are Nihilium and the other Top 50 guilds. That's because they go through content at such a fast pace.
The rest of us are appropriately geared--or even overgeared--for the content we are working on. (Note that I'm talking on a raid level. It's possible to have a few new people who are individually undergeared.)
There are four elements to defeating boss fights. From most important to least important, they are:
Gear, though necessary, is the least important of these. In my experience, every time my guild has had issues on a fight in TBC, it has been because of one of the top 3 reasons, never gear.
Unfortunately, most lower level raiders do not believe this, or at best pay lip service to it. Tobold called Gruul a gear check. Gruul is in no way, shape, or form, a gear check. The DPS requirements to kill Gruul are easily in reach of a blue-geared character who knows how to play her class.
I have been through the learning process for Gruul with two different guilds (Valarin was drafted to fill out a raid). With Coriel, our first problem was being killed by Shatters, which we fixed by using the safe spots (Strategy error). The second problem involved too low DPS, and that was fixed by focusing on hit rating and proper rotations (Skill error). With Valarin, the main issue was that healers were letting the tank die at about Growth 12 (Execution error). Note that none of these errors had anything to do with gear.
But gear is the only variable that Blizzard controls, without nerfing the fight directly. Blizzard cannot improve our strategy, execution, or skill. So they add in more gear, hoping to compensate for the lack of the other three elements.
You need to spend time on boss fights, improving your strategy, execution and skill. That will serve your guild far better than attempting to gear up for the fight. In many ways, I think that skipping Kael/Vashj for early T6 content is a distraction that will end up hurting T5 guilds, just as skipping Magtheridon for Void Reaver did.
Hard fights teach the strategy, execution, and skill required for even harder fights. Skipping a hard fight in favor of an easy fight does your guild no favors.
If you don't believe me, consider this quote from Ciderhelm's Time Management for Raiding Guilds (a superb article which completely changed a lot of my views on raiding):
What players do not understand is how real a factor time is on the guild welfare as well as their own. Spending time gearing up for new content is almost never as well spent as time actually working on that content. This is especially true in the Burning Crusade, where stat differences and gear progression between Karazhan and Black Temple is relatively small; keep in mind that Nihilum cleared through Black Temple just 3 months after raiding began. Gear is good, but it is not key. [Emphasis mine]