Interesting topic . I relaced a Yamaha Towny hub to a 17" Peugoet rim (only rim I could find with the correct 28 spoke pattern , remember the angle of the rim dimple has to match too) I used the original spokes from the Yamaha and was real lucky the spoke length was only off by a mm or two (same lace pattern , same hub flange diam). Never finished the bike but I did extend the driveshaft and outer housing so it was a complete drivetrain. Point of this was , it was tough to find the 28 spoke rim . Also I've cross matched motorcycle hubs and rims over the years and it's real expensive to buy a set of spokes the correct length. From Benelli to Montessa to BSA etc . I did relace a Mt Bike hub with disk to a moped rim once and that works, BUT I really should have bought a better quality hub with a sealed bearing ,as the others have said there is a big weight difference , once you get moving there's quite a bit more stress on those bike parts .It would be logical however to assume that good quality Mt Bike parts should be plenty strong enough to handle a moped though especially a nice alloy rim .