I think the ultimate solution long-term are assisted electric bicycles. They aren't fully electric, you always have to pedal, but when you're going up hill you can enable the assistance to help you go up the hill faster.

Think of it like gym bands to aid you doing pull ups.

If the bike could charge itself through pedaling that would be a double plus.

A lot of people don't cycle because it's slow, and they may not care about the exercise benefits. If commuting they don't want to wear special attire or be sweaty when they show up to work. However, they would probably be cool with an assisted electric bicycle if they could get up hills faster without breaking a sweat.