The issue isn't "just a file" - it's whether that file can be streamed off my device. Signal's backups are easily one of the largest files, and I don't want 3 copies of it on my phone (which is what backup currently does).

I really want the backups to stream off to my own version of the backup service, and do the neat deferred media thing which would be great for keeping long range archives (i.e. by letting them get picked up by my server's regular snapshot to backblaze).