A great concept, but there's one big problem: many official bike trails are crap.

Sometimes it's actually better to take the road, or you end up on a windy route that's near impossible to follow, debris everywhere, no right of way, etc.

I would like to try this with a "prefer offroad" option.

There are numerous options available for that; Strava, RideWithGPS, Google Maps, etc. I think the point of this project is to create something _new_ and different.