By the way, if you want any help with porting that Nautilus/Nemo extension let me know and I'd be happy to.

Writing a simple CLI to do this would work basically the same way, so I can help with that too if you like.

I'll write a full CLI at some point, I just need to figure out how to allow for plugins to work with that.

I don't have any plans at this time to write a Nautilus/Nemo extension, but it would fairly simple to adapt the one from GSConnect. Assuming Thunar plugins work in the same way, that wouldn't be too hard to port to.

Personally, I just use the Open With... dialog, which pops open a device selection window:

Ha I didn't notice 'open with', but I think this can be the solution if no other command line arguments implemented.

Then I can use this:
https://unix.stackexchange.com/questions/124811/is-there-an-open-with-command-for-the-command-line

FWIW, I think you can also use gapplication launch ca.andyholmes.Valent filename.ext. I think it should be able to handle multiple files too, so you might be able to make a script like:

#!/bin/sh -e

gapplication launch ca.andyholmes.Valent "${@}";

And call it like ./share.sh file1.txt file2.txt.