With all the changes being made to Mistweaver monks (new stance for fistweaving, Crane Stance), Blizzard will make it easy to swap between the two stances. The idea is that a Monk can easily switch when high damage unexpectedly goes out, or for phase changes, but not switch every few spells.
Is the intent with fist stance that you pick it and stay in it the whole fight or swap based on high/low damage phases?
Swap based on phase is fine. Swap in between every few GCDs is not fine. (Source)
That said, I am sure once PTR hits that people will be testing out the new stances to find the max healing output versus damage that will likely include some stance switching rotation, but even if that is the case, Blizzard could change it to be “less efficient”.