I love this app, found it a bit ago on F-Droid. I'm moving to a very rural town up north and there's nearly nothing done there. Very excited to get up there and start working on it.
every time i find myself in a rural town, i go out for a walk with streetComplete. I'm often the first mapper of those areas and it's a pleasure to complete the map and see your entries on the updates a couple of weeks later. next time you're there, you have a detailed map of the area available and you know why :)
@VirtualOdour@sh.itjust.works had a great idea in their comment above - fill in what you can, then use OSM to add missing buildings etc. They explain it better here though