I finished the Octo VCO as a Kosmo module, see Polykit Octo VCO if you are interested in schematics and PCB layout on GitHub.
I added a switch to run two oscillators in unison mode, a overall tune and pw knob and a mixer (yet to come). The mixer is for unison mode over all eight oscillators. I mainly did this to not block the mixers I have in my setup.
Now I know why they went for DCOs at some point, to get all oscillators in tune was really a tough one.