Well, since you have the choice of low- and high-contrast films, Portra really was only suited to printing from Ultra films, no?
I used it for making prints from Portra film and always had trouble with it. In fact I like Supra and Ultra a lot better.
At the same time, though, I agree that there is nothign that really fills its shoes. Kodak is starting to tighten their product lines up like Fuji already has.
Perhaps lowering the temperature of the RA-4 developer during development would allow for a reduction in contrast using Supra paper? It'd definitely take experimentation though.