No this is what this thread is for! Thanks for your suggestions! I like that idea as well. I believe I’ve made some suggestions regarding some sort of “dynamic rez” in one of the other Mercy idea proposal threads. Either way, I’m all for it. 
Oh I apologize, but I disagree.
You are making the assumptions that they couldn’t have simply given Mass res tweaks to allow for counterplay. The trade off of Mass res was Mercy having 50hp, and no decent self-defence capabilities. That trade-off was in fact, so effective, that the devs felt that they needed to buff Mercy with invincibility on her res, just to make her viable.
Making her Mass res with LoS, damage reduction instead of invincibility, a 1.25s cast time, and the ability to reset her ult counter back to 0 when she either dies before pulling off her res, or cancelling it herself, are what I find to be solutions to all of those problems, and allow for countless opportunities of counterplay.
Let’s think outside the box on how Mass res could have been fixed, eh? There were many ways to balance it. They simply chose not to do so, and caved in to the pros / streamers whining about how “unfun it was to play against.” 
~Sincerely Yours xoxo,
a Lover of True, Fair, and Fun Balance.
xavvypls 