I was at a local casino today. Many of the new slot machines are either all video, or a combination of the wheels and LCD screens. Some of the video only look like they are layers of 3 LCDs, to simulate the depth of the real machines, and to have animations look like they explode out. Then the new systems with the real wheels also have an LCD overlay for animations.
I'm not asking anyone to do it, but is it practical to emulate something like that in mame? I guess it would be no different than a multiscreen arcade machine, but I'd think the logic of layering them on a single screen would be interesting.