Summoner would not work with FFXIV current state.

[Zantetsuken]

Im down with the total idea I just want it to fit into however the combat system evolves. So even if Shiva is summoned and has its own battle actions, as long as it fits and doesn't throw off how fights are going its all good. even if the combat area itself freezes over to allow shiva to exist and turn into a mini dynamic area would work in you're design idea. That's my two cents.

Think of it more as an uber-spell rather than a pet job. The last attack part functions like an old-school (pre FFX) summon. Shiva would appear pull off a single, ultra-powerful ice attack (more powerful than any version of Blizzaga or Freeze at the same rank/level) and then vanish. This would not interrupt the battle, but merely the perspective of the players within the sphere of influence.

In short, the idea is to revive traditional FF one-shot summoning, but this time make it much more dramatic with multiple battlefield changing effects as it is being cast.

The avatar-as-a-pet idea is something that works OK in single player FF games, but in an MMO environment, they fall flat. I'd ave the pet concept for a Beastmaster or Puppetmaster like class.