No, it's not public, hence why I can't share a link nor the IP how to properly use the PCaps at their full capability, which I already wrote took me years to figure out. But I can tell you, once understood how to write your own firmware and how to deal with the raw measurement values the PCap is an amazing powerful device. No, I'm not getting any money for that statement, it's just my experience from multiple different and current sensor projects using this/these device(s).
I am not sure why they invented their own DSP in that chip. Sure, you can do all kinds of processing, but why not simply expose the CDC/RDC fully via registers and let some external microcontroller do it? This way the user would not have to mess with barely documented assembly innards.
Even having the DSP, I am not sure what the benefit of using it would be. As far as I can see if you use the standard firmware, all it does is calculate the Cx/C0 ratios and do the averaging. For me this is fine, whatever correction I will use (for the time being a linear scaling factor) will be calculated in a STM32 processor, in plain C using float variables, with proper debug support.
Of course, if you are forced by whatever reason (cost?) to have a single chip version, you could make a sensor with PDM output and linearization for whatever sensor you attach to it, but I somehow can't imagine that this chip ever will find its way in such a price sensitive application.
Do you know if there is still anyone left from the original developers who knows how this chip works? Or is all Sciosense inherited was a mask set for production?
BTW nice work with the dual axis fluid sensor! It reminded me of my first ever sensor project ages ago, where I attempted to build an electrolytic inclination sensor for cave surveying. I used a chamber glued together from acrylic glass, with some vodka as fluid. Leaked of course. I would guess for your sensor, main problems were fluid properties (wetting/capillary effect at boundaries), stability and probably topmost fluid staying inside the cavity and not evaporating.