I had fun w/ my summoner in XI.. But I kinda agree with Yoshi.. after a while, seeing everybody with the same primal summons did kinda cheapen the work it took to achieve them in the first place. The first time you saw Fenrir in XI it was like.. WOW, check out THAT summoner.. after a while, Fenrir was reduced to a Labrador Retriever.. Everybody had one, and used it to hunt.

That said, as long as there are non-primal summons available.. Carbuncle, little elementals and the like.. Then leaving the big summons as server wide seems fine to me.. though I'd still have to see how it plays out in game...

Does the instance move every-time the primal is returned or does the instance stay in the same place in the world? If it does move, is it random, or does it follow a predictable pattern? The moment you make something unique to a server, inevitability the community will find a way to competitively camp it...