A lot of threads are dealing with options syncing Scrivener files between macOS and iOS, but I didn’t find really new posts dealing with the newest versions of macOS (10.15.5) and iOS (13.5) and, furthermore, the newest version of OneDrive. So I am asking here if syncing via OneDrive now is possible or even recommended. (I am using OneDrive extensively, and I don’t like Dropbox.)
The fundamental issue is that a Scrivener project is a fairly complex structure, with subfolders and potentially hundreds of component files in a variety of formats. Synchronizing it safely requires access to the synchronization service’s low-level upload/download commands. Most services do not provide the tools that we would need.
I can’t comment on our feature roadmap, but I would say that you should probably not expect to see support for an alternative service in the short term. iOS direct file sharing is the best alternative to Dropbox at this time.