I've always wanted to see a boss battles where everyone is pretty much the same, but can buy other weapons and upgrades.
My thoughts is everyone starting off with the Power Beam - Because arm cannons are basic like a pistol, but not too low damage.
After that, you can get points to buy other weapons or upgrades like extra speed.
Hell, it'd probably be cool if the power beam could be modified to get other weapons "installed" into it, kinda like Megaman.