Isn't the bar for road-legality basically "appropriate brakes and doesn't immediately fall to bits"? I mean, we're all at liberty to buy or molish a road-legal pedal cycle of a type that even the HPV racers[1] wouldn't permit without modification.
Mass-produced machines are going to be governed by liability, and given the average bike spends most of its life rusting in a shed, it's only the high-end minority that are likely to have a reputation worth protecting and get ridden enough to injure anyone.
[1] We're less fussy about brakes and falling to bits, but have a rule about spiky bits.