@florent, sorry for the long delay in getting back to you. I'm still working on getting Christmas cards out from 2017.
two ideas:
If I can get an assessment of how reliable the rclone mount capability is, I should be able to run a second incremental backup on that mount point. The big problem there is detecting when the rclone mount has failed and halting/restarting the backup once the connection is restored. I have some ideas on how to do this and I want to chew on them a bit for writing them down.
restoration would then become easy because it's just another "network share"
If I am restricted to rsync then it probably would be safer to use full backup and move those upstream. I'm assuming that the full backup file names are the same from creation until expiration. If that's the case, then it'll be much easier to push up because rsync will only push what it does not have at the destination.
Thinking about it, it looks like I will have a lot of storage dedicated to backups, and I might be forced into having just one copy of full disk image backups that I use for the local copy and also replicate it upstream.
thanks for the pointers to the documentation I need.