If the connections in the junction box are live, then you must maintain access as per electric code. Loxone really doesn't have a good switch option for the US market mounted on either of the standard single or double gang box.
Assuming that's a gypboard wall, that your existing 2-gang box is not stuffed with lots of connections and you don't live somewhere that requires a metal junction box...
I agree that you're better off patching. We've tried other adapted plate solutions when our clients didn't want to open any walls and they always look terrible. But if you come up with an attractive one, please share!
I would cut an opening around the existing box and remove it. Replace it with one of the much smaller 65mm round boxes that match the Touch Pure. Just be glad it's not an expensive surface like tile :)