Still doesn't seem to work on wine unfortunately. I'm guessing it might have to do with Discord not recognizing osu! by itself when ran through wine (I had to add wineserver named as osu! as a custom game for the game display).
It for some reason didn't work for me and my friend. We tested the invite and ask to join feature. Nothing happens when you press the "Connect" button, but, when we tried "ask to join" it actually responded but nothing happened when we clicked "launch game"