Right now it appears to sync the least recently modified notes before most recently modified notes. This is sub-optimal as it is much more likely a user could want to access the most recent note (especially on mobile) rather than have to wait for the whole vault to fully sync before being able to do anything.
Really it should only sync changed files. Age shouldn’t matter. if it is running similar to common rsync setups it’s merely comparing modification times and/or file hashes and uploading if different.
Yes it’s syncing only changed files. But age matters because the sync can take many minutes, and during this wait, you’d rather want to be able to continue editing recently-edited files.