Hmm, it is interesting that you would think that having a hard earned team wipe being undone by a single person’s ult be less frustrating than just having a single pick be rezzed. Where it is more likely that your team has invested a few ults to pull off the team wipe while a single pick is more likely be from a primary fire or basic ability. I would think that forcing the enemy Mercy to undo an individual pick would be better ult economy for the enemy as she essentially has to use her ult to do so while you, probably as a sniper, just had to use a single bullet.
And that is the whole point of this idea, as multi rez in the past was too valuable, as it can instantly turn the tide of the battle. Yes people has argued that the enemy team should be mindful of saving some ults. But at the same time, I think the effort, coordination and even luck to pull off a big wipe should be rewarded and not be that simple to be undone by a single press of a button.
Then there are players that say that Mercy’s Ult should then be equally difficult to pull off, to give chance for the enemy to stop her. But if you really consider the fast paced situation of Overwatch, and the limited range of a multi rez, it would very difficult to find the right balance where a Multi Rez ult isn’t either op/ difficult to stop or useless/ impossible to pull off.
Hence, my suggestion for an Ult where Mercy goes into a Rez mode and gains a fixed number of rez charges. In this state Mercy is still vulnerable to kills/stuns/knockbacks, so it is even more difficult to pull off a huge tempo rez, as if she would probably only have the chance to rez only one person before getting targeted in a teamwipe.
So the more safer option would be to use Rez during the mid fight when a few team members get picked off. Keep in mind that she has to stop healing to rez each time and ensure that it is safe to do so. And this was pretty much how Mercy 1.0 was used most of the time, where like 2-3 team members got wiped by a single Ult or picked off, Mercy would use rez to sustain the fight.
Furthermore, having a Rez Mode helps the enemies as well. My suggestion is that in the Rez Mode, Mercy glows brightly (not unlike her Valk state) so that everyone knows that she can rez anytime. When she ults, her voice line “Heroes never die” can be heard across the map. And each time she uses a charge to revive someone, another voice line “Rise” can be heard across the map, so both sides can count the number of times she can rez. And in Rez mode, Mercy does NOT gain any ult charge, so if she dies before using all her rez charges she essentially wasted it.
Overall, I do feel that having the Rez ult as a mode with a fixed number of charges allows more room for balancing. You can tweak the number of rez charges, the time for each individual rez, and even allow for any buffs/nerfs in this state, further raising the skill cap potential of Mercy.