Coaster/drum brake? If so, what do you plan to do about rear braking? Then there's the already-mentioned question of what to do about the full chain case.

You see how these quickly become cans o'worms? It's not just a matter of hanging a derailleur swapping wheels. The bike was designed around an IGH with an integrated brake. Every pound you think you're saving may actually just mean moving that pound to another part of the bike.