You can seal anything with gears/chain in a case, but it makes little difference unless it’s really crap outside, chain’s, even worn chains are very efficient.
Reading had a bike hire scheme with shaft drive bikes. I never saw one actualy being used though. Which is a shame as the idea looked like an almostidentical ssytem to the Borris bikes but I guess Reading town center is too small to really need them, and they only had one docking station (at the station).
They make a re-appearance every few years, usualy as part of some design students final year project (would have to be some with a very short memory as it crops up every few years). Then don’t take off as they’re draggy and you can put a supprising ammount of twist in the shaft.