I wonder if a chain bike with a full enclosed chainguard might not be the best solution. Cheap and efficient chain, low maintenance since it stays clean and dry, no pant cuff fouling.
If the chainguard included an oil bath - like maybe the bottom part of the chainring rides in oil - then who knows how long a chain might last?
Only thing is, how do you repair a flat? I'm thinking the answer might be for the sprocket to stay with the bike when the rear wheel is removed.
Well, on motorcycles: the wheel drive chain is outside, like bicycle, and lasts around 20,000 kilometers.
The cam chain is inside the engine, bathed in oil, half as thick as the drive chain and lasts 3 to 4 times as much.