One of the approaches I don’t see talked about much is potentially breaking Mercy into multiple characters.
From the survey’s I’ve done/read from other people most of the people that play Mercy don’t agree on what they want and also most don’t actually like all of the elements of the current Mercy.
I think you could probably modify the current Mercy to be a bit more popular but, in the long term I think splitting the character would probably be a healthier option as each variant could be designed to appeal to a more specific audience.
You’ve got Mercy players that want Mass Res, Single Res, and Mercy players that don’t want res at all.
Some players absolutely love Valk and others just plain hate it.
Chain beams in Valk are also a bit controversial from what I can tell.
You’ll find that while many Mercy players do want more healing, a decent portion would actually rather have more power in other parts of the kit rather than more healing.
Valk is one of the longer ults in the game but, it seems like while some players like that about it many other players would rather have a short ultimate.
While the opinions Mercy players have don’t necessarily follow patterns some of them appeared to do so.
For example, in one of my surveys of the players that did not like flying in Valk a significant majority preferred Mass Res, wanted a short ultimate, and wanted more power in the rest of the kit more than more healing.
I think if Blizzard ran an actual survey about Mercy they could find some patterns that they could design a hero or two around to better align with what the people that play the characters want.
I think that when they look into reworking anyone they should send a survey to the people that play the character to ensure they know what the people that play the character like the most about it.