It is really a grinding operation I think. My instinct is to soft mount the router, some sort of resilient rubber mounting I think. Not too soft though, but a solid mount will lead to very critical feedrate requirements. I also think that the router should be mounted at an angle so that the side of the diamond ball can contact the glass. The end of the ball is hardly moving but the side is moving fast leading to a better grinding action. and dust extraction is a must, breathing glass dust is definitely not on my list of 'thats ok'.
Are you wanting a grinder or a score & snap system? There actually is a grinding system posted on the forum. (If I weren’t working from my phone I’d post a link.)
For cutting, score and snap. For etching - make a mask and sandblast. A decent sandblast cabinet is reasonably inexpensive.
I'm thinking more grinding/cutting, heat would be a huge issue and definitely need a proper dust system. I'm thinking cutting different mirror shapes, not standard corner cuts, but I can't seem to find too much info on it. I seen one video where they cut it in a water bath.. But that's about it. If you can share this later, would be much appreciated
As per my video above needs coolant. (water) too much heat generates plus you need special bits for grinding and polishing.