If anything, this means that Mists is farther away than anticipated. If mists was going to be running on something akin to the usual 6 month turnover between raiding tiers, they wouldn't bother implementing Strength of Wrynn 2.0, the original incarnation existed to allow guilds that reached the maximum extent of their abilities to continue raiding and progressing during the 12 month Doldrum of T10 content. They're doing this because guilds will be reaching their limits soon, and there's not going to be another relevant tier to allow players to improve their margin, so this patch is going to allow them to progress artificially beyond their actual limitations in order to keep them interested during the long wait until Mists comes out next winter.

The Beta testing for MoP hasn't started yet, nor is there any news on when it will start. My guess is we'll see some new info on MoP being released by Blizzard over the next couple of months, with Beta Testing starting up somewhere between April and June and finally MoP's release around August/September.
That's my guess anyway.

I don't know that it really means anything. It could just be a nerf that would have happened whether the beta starts last month, next month or 6 months from now.

The rationale leans toward something that would have happened anyway. Not enough groups are clearing normal/heroic DS as Blizz would like. As someone said in another thread, it's either nerf the raid or let those people who are having trouble stop raiding. Whether MoP comes out in July or November, the best option is to nerf it now so we have something to do until then.