I spend a lot of time trying to map out road trips, it would be really fantastic if we could click trails, add them to a folder and once we've selected our desired trails have mapping options such as "most efficent route"
We woudl also need option to modify the route, such as deleting stops & add stops (including custom stops not listed as trails, such as campsites, REI stores, breweries)
I'm an Apple user, but honestly, and I'm sure you know this, Google Maps seems to be what most people use.
I could also see this being useful to plan a mountain bike route. Click and add multiple trails to link and make your own route then be able to see trail data on the whole route like mileage and elevation.