I would like to see a unique implementation of summoners in FFXIV that we haven't seen before. I think what held summoners back so badly in FFXI was the overpowered potential that they could cause damage/healing/buffing/debuffing with their pets without taking any hate. This aspect loaded them down with so many shackles (abilities on steep timers, massive mp drain, limited damage/buff/debuff/healing capabilities) that this benefit was rarely worth it in most situations.
I think if summoner pets were treated as a "spell effect" or a ranged weapon rather than a being that could grab hate or take damage, things would work out more naturally. Pets could be used for sustained positional effects, such as the pet providing an AoE buff to party members in its range, and hate from the pet causing damage would be directed at the arcanist/summoner as though it was a spell cast from a black mage.
Another concept could be something similar to that of Persona, that is, whomever you have selected as your pet changes your characteristics, vulnerabilities and abilities you can perform. It's not unlike a blue mage, but as a trade-off to less flexibility in a chosen ability set, you could switch between sets a lot more smoothly.
Regardless, leaving out the weirdness of the pet taking hate and / or tanking would free up the job to be a full-fledged participant in parties (perhaps taking the role of "spell-slinging bard"), rather than an oddball on the sidelines spending most of their time casting from a limited selection of ineffectual healing spells.