Thanks for the feedback & ideas, Ronin!
I hear you re: Maths—and get the appeal of a stay-in-the-case system. The current setup is a bit limited in being able to easily create melodic sequences internally. I could do some row rotation sequencing w/ Pam's and send that cv to the mk4 in a quantizer mode—that ties up two key modules pretty well, though.
I'm a fan of Mimetic Digitalis and its approach to cv sequencing—can I get by without using a quantizer with it? I believe it can do semitones. And any other compact cv sequencers that you'd consider for pitch sequencing?
I'd have another 10hp slot for one module to work with after that—the palette allows up to 12 modules, so that'd rule out an 8hp O_C AND a 2hp module. There is the Blue Lantern O_C at 10hp—though, I am tempted to get a Basimilus Iteritas Alter (10hp) in that slot ;-)