SQLite's VFS layer is flexible and easy-to-use. There are lots of implementations (public and private) of this "use a SQLite database directly from cloud object storage" idea because it's pretty obvious how to do it when you look at the VFS functions that you have to implement. If you do a read-only implementation, it's an afternoon project. It's mostly a matter of following the VFS docs and when you're about halfway done implementing the functions, SQL queries start working instead of producing errors. The only tricky bit, as always, is caching.
I used this[0] awesome library to do just this over http. I posted more info in my other comment. I'm still exploring but so far it's been pretty impressive to me.
