The biggest hurdles then would be getting the controls to work with this.
A gamepad would be pretty bad in comparison to what we have now. IMO, if you would want to play efficiently with a gamepad, a specifc control option for them would have to be created in which you would just control the ship directly.
Expanding on that idea, let's use the 360 controller for an example:
You could use the left analog stick to control the ship's movement, the right analog stick to control the direction your turrets are firing and the direction your shields are pointing. Left Trigger controls shield up/down status, and when you activate your shields you use the right analog stick to control shields instead of turrets. I've never made a game before, so I'm not sure if this would be an easy task or something not worth tackling.
Then, I'm not sure how the current control scheme would handle on 1/2 if a screen. Probably some adjustments needed there too.
I like the split-screen idea, but it would take some serious work I'd bet.