The case looks well designed and very groove-box capable.

As far as the bottom row is concerned, I don't have any experience with the Metron + Voltera. However, if I were in the market, I'd be tempted. It looks really powerful. And the Performance Mixer might be large, but the routing capabilities plus simultaneous CV on level and pan are hard to beat at that size. I've been looking at Happy Nerding's PanMix plus a matrix mixer for my own needs. I don't think it matches the purpose built design I'm seeing here, but it's a possible alternative approach.

For the top row, what do you have in mind for that empty space? I like the idea of adding a wavefolder. And with so many full voiced modules, I think I'd want a way to dial in either a level or a modulation into specific groups of voices. That still leaves space for another effect or dedicated CV mixing.

That was a fun mental exercise. I can't wait to see what you decide.