Yes, absolutely. Jeff Kaplan actually discussed before how they have discussed setting rules for Mystery Heroes:
It seems like he’s in favor, which makes it really disappointing that this hasn’t been addressed in so many months. He mentions that some people argue how the broken comps are part of the fun, but somehow they don’t understand how it can be completely miserable for the team playing against the broken comps.
In my opinion, Mystery Heroes should disallow hero stacking, as well as carry over some amount of ultimate charge after death. (Before anyone makes the “die as Tracer with Pulse respawn as Zarya with Graviton”, I don’t mean a 1:1 transfer of percentage. I would like to see a transfer of the hidden “points” earned towards an ultimate, or even a transfer of 50% of points earned)
I really hope this is still being considered, but seeing how many months have passed since this has last been mentioned, and how out of sync the developers seem with community lately it doesn’t seem likely.