I would say that Stormblood is needed to even activate the quest for RDM, even if it's in the old ARR area's.

As for a Zodiac version of its weapon, I think it'll probably go the same way they did DRK, AST and MCH and not bother with their Zodiac or even Anima weapons. They will probably have you go through the new Eureka(sp?) zone instead.

But, you never know.