The art of Fenrir, Typhon, and Cait Sith could be a very strong indicator that SMN job is VERY close. And as you state, there are a lot more 'lesser' summons that would be good candidates for the job: Carbuncle (almost certain), Quezacoatl or Ixion, Valefor, Golem, Valigarmanda, Brothers, Tonberry King, Syldra, Catoblepas, Quetzalli, Midgardsormr, Bismark, Mist Dragon, Lakshmi, Siren, Unicorn, Seraph, etc..
As far as FFXII Zodiac Espers/Classic FF bosses. I'd like to see them in the game inhabiting a tier above the Primals. Summonable? Maybe eventually... but make them more rare and difficult to summon than even Primals will be.