I am looking for any kind of intercom to or from an exported binary.
I guess the clipboard is not practical because of the constraint (CTRL + V).
But maybe using files (R / W) or pipes. Maybe if the cartridge is invoked by a parent process, it could write to the STDOUT?

I am looking for any type of suggestion (even the most exoteric).

From the manual, standard streams or -i/-o file params are not accessible from exported binaries (would be worth a quick check though), but you can drag and drop a file or an image. That’s nice for some interactivity (trading card game, battle chip gate, etc) but not IPC.