I've long suspected that the Twelve were eventually going to get Primals, and with the revelation that Primals are actually beings constructed from the summoners' expectations rather than literal manifestations of the beings they're supposed to be, that pretty much cinched the deal for me. Through the power of Summoning, we can actually interact with the Twelve, after a fashion, while simultaneously preserving the Twelve's godlike mysteries.

As for the Ramuh/Rhalgr thing - personally, I'll be disappointed if primal!Rhalgr turns out to just be Ramuh. I'd like each of the Twelve to be a wholly new encounter. I guess it still could; even if Ramuh IS just Rhalgr as interpreted by the Sylphs, there's no guarantee that Rhalgr as interpreted by the Resistance would be at all similar.

It may be too soon to expect this, however. While the pool of classic summons IS limited, and a few of them have been "used up" by incarnating them as dungeon bosses (Cerberus, Fenrir), there's still a WHOLE lot remaining - and that's assuming that SE doesn't just create new ones from whole cloth, as they did with Ravana.