I would like to see a full sandbox mode where I'm able to have full control over both characters, and also be able to just toy with their bodies like some kind of nipple play or fingering in a lot of the positions, not only insertion all of the time. Also, a tag team mode where I can have 2 on 1 on either side.
I'd like to be able to put them into any variety of positions, and then choose what to do in each of those positions, such as holding their hands above their head and laying next to them or sitting on their hands, giving myself an array of options. Sitting behind them and spreading their legs with the players, allowing a reach around or any other kind of action that is available like teasing or breast play, and the ability to have a tag team person come in and do things as well.
You could look at SFZ for ideas and inspiration as well for actions and positions.
Also, please constrain the mouse cursor to the game window.