I don't think Hunter x Hunter will ever move to a monthly. Irregular serialization is an established, acceptable practice in the manga industry. Hakusensha has the exact same deal with Berserk that Hunter x Hunter has with Jump. Those two are the most familiar to fandom in general but other series like Oyasumi Punpun have the same deal. Homunculus did too, prior to ending this year. Other series have more regular schedules, but are also giving set time off. Weekly Shounen Magazine gives Negima an issue off every month, resulting in three chapters a month rather than four. Gantz is serialized in a weekly magazine, Young Jump, but takes every other issue off. There are even monthly series that take issues off. New chapters of Historie and Vinland Saga do not come out in every issue of Afternoon. We also forget that international fans are spoiled by Edited Mangas.
As irregular serialization is a standard industry practice, it can be assumed Shueisha does not benefit from moving Hunter x Hunter to a monthly. It likely does not benefit Togashi either. As it currently stands, he can work on new chapters while the series is on hiatus without having a short term deadline. When serialization resumes he takes time off from work. Moving to a monthly would require him to meet a monthly deadline, something he does not have to worry about right now.
Chapter count would be reduced, by necessity. Serializing twenty chapters in twelve issues would require two chapters per issue for eight months. That would be the same as writing eight at monthly length, four at weekly length. Either that or he would be serialized for twenty straight months, before taking another hiatus. That does not seem like it benefits Togashi, nor does it seem more sensible than serializing twenty chapters a year in a weekly and getting time to work without a deadline. Considering he also had special treatment for Level E (serialized in Weekly Jump, but only one longish chapter a month), it seems unlikely that Shueisha will take a hard line with him now. Togashi is semi-retired - he's been a professional mangaka for almost thirty years and his wife is loaded. Nothing has indicated he wants to return to any sort of regular publication.
