There are already players in the Hall for far less than what Mahomes has already accomplished. If his career were to end this year, and I would still think he belongs in the HoF eventually.
After all, there's no objective measure for who should and should not be in the hall, as far as I know. It's called the Hall of Fame: "Hall of Fame", not "Hall of Stats", even if stats play a big role, the most important criteria are far more subjective and even based on what Mahomes has accomplished so far it would be hard to me to imagine him not being strongly considered even if the rest of his career is not so great.
BTW, people are acting like the wheels have fallen off this year because of the INTs. I agree that it's not as good as it has been in years past, but it's not like the wheels have completely fallen off. We're still only halfway through the season and he's on currently pace to throw nearly 50 TD's again