Yea the BSP and Keystep and SQ-1 are standby essentials for modular gear no doubt bang for the buck. Ideally I'd want a sequencer and sampler as part of the modular system as I hear they are lot of fun in modular gear!
I would love to try out a Carbon sequencer. For now been busy learning my Octatrack and 0-coast as they pair up well. I can sequencer/sample and mangle both for lot of possible options in a small footprint.