I definitely don't see the "New School" pet style summoner working well with in the construct of xiv. how ever i can see the old way of using the spirits as single shot spike damage or buffer/debuffer working quite well. I really do not see the primals wanting to hang around and have tea with you. they give off the air of lending you a bit of there power to use as there disciple though.

You can see this in action with the beast tribes. All of the Amalj'aa attacks are firebased, we know from interaction with them that they are under the sway of Lord Ifrit. Ifrit being the sole primal that players have had any interaction with so far (if you have progressed in the story far enough). Kobalts use earth based abilitys and heck 90% of there attacks have Titan in there name. Titans flesh, rage, ect. The Ixtal have a Wind based theme to there attacks and they are under the say of Garuda. and one can assume that once the sahagan stop hiding behind the reavers and show there faces they will have a water based theme being under the influence of leviathan.

I can honestly see characters being able to manifest the powers of a primal or guardian to perform various actions and then at higher ranks for a summoner proper being able to actually call a physical embodiment into existence to perform a damaging attack before that embodiment vanishes. Once again i go back to the beast tribes. while the rank and file can draw on there god, its only the clergy proper that can Summon them from the astral realm.