Wouldn't just good screen sharing solve your coffee table problem?

Just have the coffee table iPad be a display for your own iPad. You could even have a virtual iPad on your mac that you show on the coffee one if you don't have your own.

MacOS has 'high-performance' screen sharing using hardware encoder/decoder now. Windows has had this for years and it's so fast it's like actually using the remote computer. It's not like old-school VNC, the only real functional drawback is that you can't leave wifi range.