I’ve spoken with someone who had access to their $30K full size grading desk/keyboard and it had conventional rubber domes underneath the keycaps. The keycaps themselves were sold for ~$600 as a kit. No idea if GMK was involved 
They’ve specifically referred to the newer editing keyboards as having “e-sports grade switches” in interviews before. My assumption is that they’re some variety of Cherry/Gateron Reds or Blacks.