I always hoped (maybe over-simplistically) they'd make something with a mag that would hold the 12g CO2 powerlet and a regulator (and maybe pressure-regulated reservoir) would reside on the gun.
I swapped out the piston head on my mini uzi (the piston head mod) and performance increased dramatically: I can fire off about a mag and a half (~50 BBs) in quick consecutive bursts with pretty much no ill effect (asides from a bruised ego from the abominable grouping resulting from the recoil heh), so I figure if it was regulated down to game-safe velocities it would have plenty of power for a "standard" ~68 BB locap under most playing conditions. Either that or two "realcap" loads.
Anyway, IMO, that combination would have incredible appeal to milsimmers. Powerlets aren't that expensive when you buy them in bulk (about 75¢ a piece), and milsimmers don't generally spray and pray all day, so it would be very acceptable.
What, a guy can always dream, right?