Hey @LN, thanks for laying that all out so clearly!
It pretty much all matches what I've been thinking except for one adjustment: I'm working on taking @langstonsmith's last branch and getting the Mapbox implementation up to feature parity with the Google and OSMdroid implementations, so that it can be a complete replacement for OSMdroid. I've run into a few tricky bits with that, which I'm discussing with @langstonsmith over on the other forum post. These mostly have to do with the drawing and manipulating of markers (symbols) on the map; I've filed a few issues on the Mapbox Annotation plugin.