Kinect sounds like a lot of work. I'd just figure out which pixels represent the corners of your neg carrier mask and write a little bit of software that displays the mask scaled to fit that rectangle. There are lots of tiny arm-linux boards available cheap now, some of which have integrated LCD-driving electronics; try the beaglebone series or maybe the Raspberry Pi (though that's only HDMI out).

Don't forget that if you use a colour LCD, you get an extremely powerful multigrade tool that would allow you to apply different contrast to different parts of the scene. And if the LCD has enough contrast of its own, it can act as a precise shutter, which means the controller for it becomes your enlarger timer. Port some f/stop timer software (see my sig) to it and you have IMHO the ultimate darkroom tool. Making me jealous already just thinking about it.

One of those crappy $100 7" android tablets might be a good source of LCD and controller CPU.