Really guys? Really? Oh come on.
No support at all.
1) osu! is already hard enough with one mouse,
2) We have enough game modes (four!) to entertain us for a moment, and
3) Some people definitely can't stream with their mouse (me included), because of the way they hold their mouse for example, so this game mode would be very troublesome for them. I know, "it's only a matter of practice" you would say, but this would be VERY frustating for us to see that this would favour mouse-only people and discriminate mouse+kb players.
...and 4) I don't want to buy another expensive Razer mouse + mousepad, really. Mouse that besides will only serve for this particular mode, how convenient.
This idea is pure madness and coming out without any thinking at all.