I cant see them adding arcanist to healer que because if carby dies than your boned. Im sure many people will dislike that. They should just be a support dps like archer.
The same could be said if a Conjurer dies, but such is the nature of healing.
However, there is lots of room for conjecture. It's possible Carby can't die as long as the Arcanist lives (and I'm rather partial to this system since pets with hp cause all sorts of painful balance issues). We don't know if Carby can fight, hold hate, take direction or acts independently.
I do know the Summoner job in FFXI was terribly flawed (having leveled it to 95). Since avatars could act as indefinite defenders of their masters as long as there was enough MP and time to recast, they were nerfed to the point of being incredibly ineffectual compared to any job where the person took and risked death from direct mob hate (which I don't dispute, but it did place summoner in an incurable conundrum). As a result summoners weren't really good at anything, even among generalist jobs, apart from some oddball uses and heavy use of a healing subjob .
So I'm hoping they make a break from this approach and come up with something that puts this job back into the game in a way that's balanced with all the others. The potential to beat mobs hate free is more of a curse when you consider the cost that must be paid.