Hitmonchan's largest niche will most likely be as a Rapid Spinner to differentiate itself from other Fighting types like Gurdurr and Sawk. Being able to get off a guaranteed rapid spin with Foresight is a huge and was a large reason as to why Hitmonchan was considered the best spinner in LU last gen (Pokemon Online's version of RU). It also has a good priority move in Mach Punch, allowing it to pick off quite a few threats such as Klingklang, Kabutops, and Tauros. I'm thinking Hitmonchan's main set will be this.
Hitmonchan (M) @ Fist Plate / Life Orb
Ability: Iron Fist
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Rapid Spin
- Close Combat
- Mach Punch / Foresight
- Ice Punch
Pretty self explanatory set for the most part. The choice between Foresight and Mach Punch depend on your team's needs (priority to revenge kill certain mons vs guaranteed spin). Pursuit support from Skuntank will be almost mandatory for Hitmonchan, as it struggles significantly in damaging psychic-types.
Overall, I feel Hitmonchan will largely be a niche mon. As a rapid spinner, its inability to defeat garbador and to a lesser extent Mesprit are large issues (you can run EQ if you really want to hit Garbodor, but its a useless move otherwise). As a fighting-type, its inability to damage psychic and ghost-types are also large problems. However, Hitmonchan still has the core benefits of both a Rapid Spinner and a Fighting-type, which no other mon in NU has, allowing it to fit onto specific teams that cannot fit both.