Really interested to see where this goes, just wanted to share my thoughts.
On paper, Gateron optical should be ideal for a gaming daily driver (smoothness, no debounce, MX keycaps). It would be game changing to put together a nice optical keyboard.
I am really glad you are working on a PCB, thats a huge piece. A QMK compatible, HHKB/Tsangan style PCB would be perfect for me personally. If I had one, I would put it into an MX hotswap case with an integrated plate (where the PCB screws into the plate).
I couldn't find a datasheet for Gateron optical switches, so I bought an iGK61p and a bag of silver switches to check them out. As I suspected, there is absolutely nothing to keep the switches in the PCB, it is going to be entirely on the plate to keep the switches in place. The good news is that it looks like the distance from the top of the plate to the bottom of the switch housing is the same as it is for MX switches, so I think there is a good chance MX integrated plate cases will work well. I just hope the standard poker pcb mounting holes will be sufficient, because I don't think you can afford to have your PCB flex much with optical.
And of couse I would try the new switches too! Also if you really want to go above and beyond with the PCB you could include an optional JST connector for a usb daughter board, so it is compatible with some high end MX cases.
Hopefully some of this was worthwhile. Keep up the good work!