Programmatic control would be useful to me. I wasn't able to successfully send a "switch to slave" type command to Input Director using AHK at all, using any of its sending methods, and with that Logitech option enabled or disabled. Switching back to the master would be even more difficult, as my inputs would be sent to the slave at that point, and so the slave would need to tell the master to return the pointer.
While I'm here, I'd also like a way to send keys to specific hosts. I'm currently using some unused scancodes as key bindings in ID as a way to send keys to a slave while the pointer isn't there, which isn't really ideal, and something more versatile would be nice. And a way to retrieve which machine was currently being controlled. If it was up to me, something a bit more "direct" than a command-line thing would be good, as that'd be kind of slow. Maybe good old Winamp-style WM_COMMAND/WM_USER messages? That should be easy enough to use from other programs, and a command-line program could maybe use that too.