Obviously I am all about #3.

Even though a few people keep preaching that it would be a hard balancing issue I couldn't disagree more.

My reason for picking #3:
Mainly: I like/love petjobs! They are very tactical and provide very nice gameplay mechanics, helping to kill off some of the tank n spank mentality that most MMO players are heavily grounded in.

Also: I believe that SMN as a petjob gives the Primals themself a lot more interesting utility rather than just having them as a single cast spell or a storyline mechanic. SE can gain a lot from allowing players to interact with summons in this manner. They could make the summons AI very diverse and increase the type of interaction that the summon itself adds to a party/group based battle environment.