People have already said this but *it's a really good idea*
I thought this might make a good co-op game (in campaign). Play as any member of the squad (SP or co-op). Or have a different player character (squad member) for each level ( i.e. level 1: Boss, level 2: Scorch, etc.).
Another thought... Perhaps give each member of the squad an advantage in their area of expertise; for example, Fixer slices faster than the others, Scorch carries more AA rounds, Sev carries more sniper rounds, and Boss gives the orders (like the original).