Removing the BBD and the Sequencer, as you suggest, frees up 20 HP.
A few common ideas for 20 HP modules include, Maths, Doepfer Matrix Mixer A-138m, something spicy like Morphagene, Sealegs, etc. Not sure this would be best use of that space, but it's something to not overlook.
Breaking that 20 HP down into several modules will probably get you more mileage, but that'll be your decision....smaller module ideas that might add something include Pico DSP (erica), some sort of Euclidean Rhythm generator (2hp makes an okay one), noise and/or random voltage sources, and the various Doepfer switches/utilities.
You don't necessarily need to fill all 20 HP right away.....you could pick up, e.g., an Euclidean rhythm generator, the pico dsp, and see what you feel is missing after patching for a bit, or until it becomes obvious.
Hope this helps stimulate some ideas! Good luck!
“You must have chaos within you to give birth to a dancing star.”
― Friedrich Nietzsche