No front derailleur. 1x10's, 1x11's, etc.

Speedhub

Those are pretty expensive though. At that price, why don't I just get a Rohloff Speedhub, which has all kinds of advantages?

Possible issues with the SpeedHub:

Ways to make the Rohloff work with drop bars:

Speedhub cost

Extra costs, other than just the internal-geared-hub itself: