Strava has a feature called the "Route Builder" that allows you to build a route then export the GPS track to your device of choice.
MTB Project seems like the perfect platform for a similar function. Allow users to create a custom "ride" from existing trails, then send it to their app to follow once out on the trail. Basically the same thing as a "Featured Ride" but shared privately rather than publicly.
My reasoning is that if I'm going to a new area, I may or may not want to follow a Featured Ride - I might be looking for something shorter/longer/different than the Featured Rides listed, but I also wouldn't want to create a new, public Featured Ride without having ridden it yet. Allows users to create private rides would help planning and navigation on the trail without cluttering up the public ride database. Right now I reference trails on MTBProj and then create the route in Strava, but it's a little clunky both in creation and out on the trail.
Yeah, I would love a way to build rides using existing trails to upload to my Bike GPS.
I definitely download and use the rides provided on the site, but when that doesn't match what I want to do, then I build ride tracks in RideWithGps, typically using the open street maps layer (when open street maps has trails on it) and use that to load my Wahoo Element with the track. This only works sometimes as a lot of the time the basemaps don't have enough trail info on them (or if at all) to create a ride properly.
I'm sure it's quite a development effort for this sort of feature. I'm sure it's something that wouldn't be built easily.