Is there a glass-smooth, shiny, build plate for the X1C (or P1S)?

It’s possible. I’ve used float-glass build plates with my old Prusa Mendel clone, and am competent at glass cutting. The nozzle wiping area would be tricky to manage. I used to do stained glass work, so might be able to cut glass in a way to provide a wiping area. Not at all sure how well that will work. It would be interesting as an experiment though.