Conceptually, this is interesting, but I'm not sure exactly what this cab is for. Is this a "voice", or is this where you intend to do the signal conversion?
One other point about biosignal work: it's not merely a matter of "connect ficus tree to input preamp". In order to amplify signals of this magnitude, you'll probably wind up needing far more gain than a typical Eurorack input can offer, plus a good bit of signal cleanup. For a decent older example, see l80AAOSwJU5drCq6" target="_blank">https://www.ebay.com/itm/EEG-POLYGRAPH-DATA-RECORDING-MACHINE-GRASS-MODEL-79D-PARTING-OUT/153691498905?hash=item23c8ba2999l80AAOSwJU5drCq6 What you choose for electrodes and leads will also be important; some work well for one application, but are utterly useless for others.
You'll mainly be looking at EEG gear for your signal pickup, since those systems have the necessary amplification factors to bring the biosignals up to a relatively usable level. They also tend to offer the HP/LPFs needed to remove noise and spurious signals on the input...and believe me, you WILL be wrestling with that noise/garbage issue, since it only takes a few feet of unshielded cable to pick up enough electronic crap at the required amplification levels to render all of your bioinput totally useless. However, if you're uncomfortable with electronics that go WAY outside typical synth gear...well, you're just plain screwed. This is very much one of these control methods that requires going outside of most synth users' comfort zones.
It's an interesting idea...one I've tinkered with on occasion. But at the same time, it's an infinite rabbit-hole...so be forewarned!