I think lowkey hits a good point. What really is there left that falls under the monk umbrella? We have Avatar monks, ninjas, kung fu fighters, long death death cultist monk, and pew pew laser monks.
Pretty much all the suggestions are just tweaks to one of the existing subclasses already. So maybe not a subclass, but a list of additional powers for the Avatar monk. Maybe s weapon monk that gets access to fighting styles and weapons that count as monk weapons, but I'd treat that as more of a feat than a full subclass. for example:
Monk Weapon Master feat: instead of the stat bonus, the additional weapons you are proficient in are now considered monk weapons.