P.S. Kodak C-41 Pro and ECN-2 are almost IDENTICAL in contrast now. Literally within a couple of percent of each other. Vivid Fuji neg in ECN is more contrasty than C-41 pro. So all you need is a different filter pack; no chemistry modifications required for RA-4 or ECP-2D.
Can't say I do much optical printing of ECN-2 negs onto paper, but if the contrast is the same on the print stock. . . the contrast should be the same on paper too, right? I can't see any reason to modify anything, unless you think Portra prints too flat too on current RA-4 stocks.
It's really the problem of the PAPER SURFACES being discontinued, not any mismatch with the film. Where is a Portra Paper, Supra paper alternative? That is where flashing, pushing chemistry manipulation where be necessary for optical printing in the very near future.
All that is out there is Mitsubishi I assume high-con paper Fuji PIII Crystal archive pro and CA amateur paper and Kodak Ultra or Edge (basiically the same thing, just tighter tolerances on the Ultra). Is there any such thing as a low-contrast, optical compatible RA-4 paper?
Only near alternative I can think of is a flashed paper to bring the ocntrast down with and/or a developer tweak for the RA-4 chemistry. Maybe the contrast of hte paper can be lowered by just tweaking chemistry. Flashes have the nasty habit of eliminating true whites on prints.