This is a pretty interesting question @jamesallisters. I'm definitely not the best qualified to answer on the forum, but I went ahead and put together a rack (based on yours) to think about how I'd tackle this problem.
My theory (though I'd love to hear what others think) is that I'd want:
1) a ton of modulation: so I added the Ochd, the 4ms Quad Lfo, and the WORNG Vector Space, this in turn would make me want
2) a lot of VCAs: so I added the 4ms VCA Matrix
3) a quad effects path, so I added two Erica Synths Pico DSPs which are each stereo, and the Qu-Bit Tone
4) a ton of potential voices, so the Quad Morphing VCO and the Chord
5) something to fill in all the gaps that are missing, so a Disting EX which can be used in dual mode
6) one more inverter just in case, and
7) some way to manually control quad panning, so the Planar 2.
Anyway, I'm not sure I'd suggest you buy this rack exactly, but hopefully there's some useful ideas in there!
my tunes: https://stevehand.bandcamp.com/