Please if you need to save backup files from the target, I agree maybe a loot isn't the best option, but I don't like the idea of allowing the user to specify any location to save the data really.

I think would be a good idea to use maybe the metasploit log directory to save the backups. And do a report_note to point which backups and where they have been saved. I've seen it done before in the persistence post module, which now is a local exploit:

https://github.com/rapid7/metasploit-framework/pull/1458