Saw something in general that got me thinking. If they (blizzard) don't add some firm gating, how do you expect raiding to have much in the way of longevity. The general complaints have always been that it would take so long to get all your loot drops or your secondary gear set. However, since gear will now change with spec, thus conceptually decreasing loot tables, the speed of progression via normals and heroics seems likely to be a problem.
I am not too experienced with LFR but that seems to be losing loot so while it would have been a potential blessing there it seems unlikely to have any effect. Also, as ive not raided much in a long time perhaps im out of touch but still am curious as to what you think.
Your chance to get loot at all will go up, but your chance to get the "perfect" item will be far lower than it is now, to the point were full BiS will be nearly impossible to achieve.
This should ensure that you can get enough gear to function fairly quickly, but never reach a point where a raid doesn't hold any potential upgrades for you.
Also, only primary stats change with spec, everything else stays static. For optimal gearing, you'll still want different gear sets for different specs.