What I think arcanist/summoner will be

[Onisake]

additional summons i expect to be linked to the limit break system.

you may have additional summons based on level. IE: summon avatar is gained at level 1. at level 20 you gain enhanced summon avatar that allows you to summon fenrir. but more than likely it will just add abilities to carby's roster. and the summoner job will be where you get some of the cooler stuff. maybe we'll get sylph as a sustained summon.

we will likely be restricted to 'terrestrial' summons. such as Carby, Phoenix, Fenrir, diabolos, and bahamut. as part of either sustained summons or limit breaks. 'celestial' summons are tied to beastmen, like titan is the guardian deity of the kobolds. it doesn't make much sense for us to be able to summon him. We do know that Siren has been unofficially confirmed through concept art. but she could be the guardian deity of sahagin like beastmen. but then where does leviathan lie?

We have seen creatures resembling both bahamut and Diabolos in the trailers (both for ARR and 1.0) so i do expect them to make an appearance in ARR at some point.

[Reynhart]

we will likely be restricted to 'terrestrial' summons. such as Carby, Phoenix, Fenrir, diabolos, and bahamut.

"Terrestrial" summons were tied to the FFXI lore. Final Fantasy in general doesn't make a difference between summoned creatures.
Besides, we've already seen Bahamut in the opening, and it's skeleton rests with a wrecked airship in Mor Dhona.

[Naraku_Diabolos]

additional summons i expect to be linked to the limit break system.

you may have additional summons based on level. IE: summon avatar is gained at level 1. at level 20 you gain enhanced summon avatar that allows you to summon fenrir. but more than likely it will just add abilities to carby's roster. and the summoner job will be where you get some of the cooler stuff. maybe we'll get sylph as a sustained summon.

we will likely be restricted to 'terrestrial' summons. such as Carby, Phoenix, Fenrir, diabolos, and bahamut. as part of either sustained summons or limit breaks. 'celestial' summons are tied to beastmen, like titan is the guardian deity of the kobolds. it doesn't make much sense for us to be able to summon him. We do know that Siren has been unofficially confirmed through concept art. but she could be the guardian deity of sahagin like beastmen. but then where does leviathan lie?

We have seen creatures resembling both bahamut and Diabolos in the trailers (both for ARR and 1.0) so i do expect them to make an appearance in ARR at some point.

The way I see it is that after SMN is unlocked, every 5 levels allow you to battle another summoned spirit to acquire and then use, just how the DoW/DoM jobs were for obtaining abilities and AF.