There are many, many ideas for different merc ideas in the Merc Suggestions page that I don’t think that we’ll run out of unique ideas.
Case in point: most of my ideas usually are unique compared to what the other mercs offered. Riot shields for pushing instead of defense, an armor based (overheal HP) medic that uses a sniper rifle, and Stratus.
Another thing to add is the fact that the game’s amount of variety, in spite of having 21 mercs to come, is surprisingly low. All fire supports have assault rifles, most recons have snipers, and Fletcher’s literally just an insane combination of grenades and doubled capture rate.
The last one in particular grinds my gears in the wrong way. As long as Fletcher (and by connection Proxy) is in his (their) current state engineers would remain with major power differences between the strong and the weak. Engineers are supposed to have a wide variety of defensive abilities that would complement doubled capture rate.
But in order for Fletcher to be balanced, he needs a medium range form of attack, thus the problem his presence has in the game.
So this game’s real value for me is as a teacher, to show me what went right and also what needed to be improved and why they aren’t going to be improved.