I often cannot see people using [lore] any other way than to casually say no without putting more effort into the conversation.
Just about every idea thread I've ever seen has people saying "no because [reason]", whether that reason be lore or they want something else fixed first or something else added instead and to be frank those posts aren't worth the time it takes to make them. Everything in this game is stuff that people just made up. If the devs have a cool idea they absolutely have to put in the game they'll find a way to make it fit. When it comes to random player ideas they're just that, ideas. We're essentially pissing in the wind but it's fun talking about things that could be and how they might work and that's as far as it goes.

Anyway, my suggestion to lore if the void is absence then might be to say that the void mages use the absence of aether to damage their foes.

Personally I would suggest if you must keep the voidsent part of the job, actually demons being bound to you, that the lore of the job is more accidental.
Pretty much the only information I could find on Void Mages is that they summoned Voidsent by opening rifts, and there aren't any Void Mages left. So it's a very open design space, but I do think summoning Voidsent is important to the job. That being said I wouldn't be against a version that doesn't use Voidsent because it's essentially an entirely new job that can be taken in many directions, this is just my take on it. There's something to be said for the mechanical aspect as well since there currently are no jobs with expendable minions, or a focus on dots.

Using the absence of aether is a cool idea, I don't think anything like that has been done before. It's like anti-aether. Could be used like a vacuum that drains aether from things, a controlled black hole of sorts. That certainly has potential.

Something I'd like to see for such a job if it happens too though is being questions, perhaps with multi-choice answers that the game then responds to. It's just a game so we shouldn't take it too seriously but I would find it interesting to have a semi-real life discussion on using powers that may be just TOO dangerous and is it morally acceptable. Maybe add a few lines with making the Scions uncomfortable.
Yep, for sure. I imagine unlocking the job would give you the choice of saying "this is too dangerous" and turning down the job, more stuff along that line would be good too. The Scions most definitely wouldn't like it and Cait Sith might even become your enemy for using it - at least until you can convince them you're only using it for good though they'd still be wary.