30, I can't imagine. He benefits from being dominant in a cuspy period right now-- his fellow demigods retired or in serious decline while the wunderkind are marvelously talented but not quite ready to take over. He has maybe another nine months to a year until they do. After which the GS championships will dry up fast.
Even with an ideal situation 26 or 27 seem like the new ceiling to me. My guess would be that he ends up with 25. That's higher than I thought after Australia, though.
I think this is right. He's 36, battling near-constant little (and not so little) physical issues, and facing kids who haven't quite found that world-beating form yet (although Alcaraz looks the closest), and it will be tremendously hard to have to get through, say, two or three of them to get another major. I would not be surprised if yesterday proves to be his last major title ever. And I say that as a big fan.
Having said that, it also would not surprise me to see him with 2-3 more by this time next year, either. Whichever way it goes, it should be good for us tennis fans.