Probably main tbh
I could see Moira + (any other support besides mercy) coming in to the meta just like Ana + (any other support besides mercy) was during triple tank
Doesnt moiras healing beam do the same amount of healing as mercys?
*edit*
I googled it and she does 20 more healing per second than mercy(mercy does 60 per second) so she probably could mainly heal if she isnt trying to dps