They posted expanded explanation and it makes even less sense.
http://www.wowhead.com/news=253031/legion-respec-costs-removed-talent-changing-restricted?refresh
Where are they even going with this? Making you go back to Dalaran between bosses isn't "meaningful" in my book - it's just a pain in the ass.
Except there is no customization and differentiation. They've pretty clearly tried to direct the new talent system in a direction that makes different talents useful in different situations - in which case your talent selections are determined entirely by the encounter if you're trying to play optimally. And the funny thing is that they even failed to do this in most cases - there's generally a "best" talent build and that's what you choose, because you're probably swapping specs between single-target and AOE fights if you have another one available to you!
We could never switch talents freely, at any time, and in combat. Literally no one is asking for that. Why are you even bringing this up?
No! NO! There would be no actual variety! There would be the people who picked the best build and the people who fucked it up for themselves! That's not variety!
Who the fuck cares if people switch talents for trash?! It's fucking trash! And if the dungeon fights are sub-1-minute, it would be faster to just mow the shit down instead of switching talents and rebuffing before the boss anyway! And they're fucking dungeons, not Mythic raids!
People are going to be switching talents before raid bosses unless you make it so prohibitive that switching talents might as well not exist - so why are you just making it a pain in the ass?