Currently I am raiding in a mediocre guild, we are not one of the hard progress dudes, but usually we farm normal a few times, then go heroic and farm that a few times and then go slowly to mythic. Sometimes we clear mythic before it gets nurfed, sometimes we don't. It depends.
Usually everyone I know changed talents for each boss, often even between tries. I changed talents for Mythics and challenge modes and so on.
But with the new restriction I completely stopped doing that. I just looked up what seems like the best overall choice for most situations one time when I got to 110 and I never changed anything after that on two characters. The same goes for basically my whole raid group. The costs for respeccing in-raid are simply way to high, so we just don't do it. And since I am not doing it in a raid I see no reason to do it when I go to mythics. And don't get me wrong, this seems to work completely fine.
But is this actually intended for everyone who is not a total progress raider that wants to down everything as soon as possible?
What is your experience with the current restrictions? Are you changing talents or did you also go for a cookie cutter build?