Now you really got me thinking,
This morning when I got up I looked at the build again and noticed that there are almost no VCAs.
Then I read your Post and took a look at the Skylab.
I think that you‘d be best of trying to replicate half of the Audio Path of that thing and definetly drop one random source in favour of a quad envelope (closest Thing in Euro is probably Quadrax plus Expander) and add VCA‘s dedicated to modulation.
Also you completely omitted the Frequency Shifter.I think thats a pretty crucial one. Luckily Doepfer just put out a very reasonably priced one, yes it‘s a little small, but I think it would be your best bet.
Now I tried to do a complete overhaul that makes sense to me, while keeping the modules as big as possible and looking at the Skylab.
I actually really dig that build, luckily I don‘t have 5 grand to spend on modular right now ;).
Wish you all the Best
Chris
PS: still did not Update, need to click link again.