If they all have to agree then I can’t see it happening because it seems like only Louis and Liam would actually do it and even Louis I’m not sure about.
At the beginning of the hiatus, Louis initially did seem to be gunning for a One Direction reunion to happen. I think that as he developed and found his own footing, his opinion of that changed. I get the vibe that while he wouldn’t decline a One Direction reunion if it came knocking on his door, he isn’t itching for one.
Niall has always been open about the possibility of a One Direction reunion, but he also isn’t itching for one. Harry has said that he’ll never rule out a reunion, but I don’t see him doing one until he’s at a pause in his current career trajectory.
That leaves Liam, who doesn’t currently have a solo career to speak of. Out of the four of them (I’m fairly sure Zayn wouldn’t touch anything One Direction again), he’d benefit the most from a One Direction reunion. At least with a reunion, he’d have a focus, something he severely lacks in his solo career.
I don’t see a reunion happening anytime soon, to be honest.