SE has stated they dont want a true "pet class", so without going into that

1) the final boss of.. was it Xelphatol? He has his own set of moves, but 3 of "his attacks" summon garuda to do a quick hit then go away. This would be closer to summoner in most final fantasy games (the summon comes down, hits, then goes away). Imagine death flare being a bahamut summon, pain flare being a different summon.. now that I think about it most of the current oGCDs would be fitting. This is mainly an astetic change (and roll some of the current pet abilities/utility into the summoner, as well as a flat DPS increase)

2) FF10 summoner. The summoner is weak by themselves, but can take the form of a summon gaining access to new abilities. As cool as this would be, it may be too potent. Channeling titan would give tank like abilities, channeling ifrit and becoming a melee DPS, a caster as garuda and so on.