Would it be possible to create custom pcb and actually build Topre board?
Theoretically possible? Yes. Practical? No.
Keep in mind that like most capacitive switches the switches themselves don't attach directly to the PCB, they just kind of sit on top of it. It's the case that actually keeps them in place. So for a PCB with a different layout it is necessary to design a new case to go along with it as well.
Also the rubber domes are typically in the form of a single sheet, designed so that the domes are were the keys are in a given layout. Now it
could be cut up and basically still work (which is actually what people do for some of the aftermarket replacement domes out there), but some people would be reluctant to do that. So you might have to make domes as well or just direct people to some of the existing aftermarket options.
With all this in mind you're basically talking about making an entirely new keyboard. The only parts you would really be preserving would be the springs and sliders, neither of which are terrible expensive or complicated. And I guess keycaps as well...though that could also be an issue for alternative layouts. I guess you could go all in and make new sliders that were MX-compatible as well at which point literally the only the that would carry over would be the springs...yay?
