This project is looking great so far, I'm a big fan of anything outside of standard game dimensions!
It's interesting you bring up the shaker ball games and Varkon. I got to play a Varkon for the first time recently, and I was surprised how good it was. The vertical effect was a lot more effective than I would have thought, and changed how I experienced the game significantly. I've been thinking about making a mirror/"vertical" game myself since, there's a lot of design space in that format I think.