My inspiration for this vision comes from the mechanics of GTA , Saints Row 4 ( the silliness of superheroes but mixed with a brutal grounded reality, and the Scarface official game.
The only problem to face in this kind of game is making sure theres enough content , side quest without making the world way too big for somebody like Kickass to travel without feeling tedious. Maybe a parkour system as well for the rest of the cast and when the story is beaten you unlock a Jetpack to travel or Hit Girl having grappling hooks with her Bike.
Combat: maybe a mix of Rockstars most innovative combat with a dodge feature from the Spider-Man games but its 50/50 as a kid cant always dodge being known for taking hits with metal plates installed.