Stephen, I think you and I talked about this years ago, not sure, but given that the inner pump liner of the Paramo system is a constraint on usability of the system because it is provides too much insulation for most rainy conditions in the US, I puzzled long on how to replicate the function of the pump liner with less insulation.
One idea that I had was layering a Finetrack elemental layer over a thin base layer to replace the pump liner. The hydrophobic elemental layer would provide the hydrophobicity, and the standard thin baselayer (or Brynje) would provide a gap between that layer and the skin. I think a thin base, already assumed worn, would not be made appreciably warmer by the additino of the super thin Elemental layer mesh fabric, but would provide much the same hydrophobic function of shedding any moisture that got through. But I’ve never extensively tested this combo.
I did do quite a bit of testing of “roll your own” Paramo using various windshirts paired with either a furry fleece that I treated with Nikwax, or with a bespoke shirt made of Paramo Pump Liner fabric, or with Paramo’s Enduro Fleece stand-alone product.
The windshirt chosen was the critical piece, and DWR failure usually resulted in water ingress, as did typical windhirt vulnerabilities – cuffs not sealable, hoods don’t shed water that great, etc. But otherwise, these roll your own combos work pretty well, and I did some long hikes in steady rain using these with only minimal ingress. In general, an ultralight full-feature windshirt + pump liner shirt came in about half as heavy as the lighter Paramo one-piece, off the rack options. But none of these combos worked as well as the Paramo one-piece jacket systems, which are fairly refined for this function, although sadly too darn heavy for ultralight backpacking unless it is in sustained, cold rain, which is not as common in the States as in UK.