My guess is that Shiva will be associated with either the Gigas, like the ones in Coerthas, or the dragons that the Ishgardians are at war with. From the existing lore dealing with the dragons it seems they are at least as intelligent as the beast tribes and not just mindless lizards, and they seem to be associated with the colder climate areas of the game. Ishgard will eventually become another city we will get access to, but maybe not until the first expansion or at least a couple content patches away.

There may be was seems to be a pattern of two per city state but I honestly wouldn't count on it.

There is also a chance that there may be more primals that the traditional ones. Odin for example is considered an elder primal if I remember correctly so there could be a bunch of them yet to come.