I'm happily using the union remote to ship off my backup on several different cloud providers.
I can see during a sync that a few files at the same time are being transferred, great.
is there a way to know (e.g. in the logfiles) or, even better, see (in the terminal) on what remote my files are being uploaded?
You can try turning on -vv logging and see if that helps. I can't remember if union writes enough there to be useful.
Anything else would require a new flag. It wouldn't be difficult to make a new flag to show the remote names or full path in the logs and the progress.