Hmmm, that would actually work.
Especially the resetting part.
As it currently works, you have early puller, and no one wants to miss out, so people keep attacking even through someone else is trying to reset the boss for others,
and yelling at people to stop attacking, which most will do, but some won't, then everyone keeps plinking, and then goes back to full attack mode.

The big question here though, do the devs WANT to mess with old world bosses?
It's probably a wait and see sort of thing, although with a mechanic like that, a sliding scale or additional player reset mode, they'd have to go through testing to make sure it doesn't bug out, which I could easilly see happening.