I have a feeling Buggy's going to end up with Imu's job by the end of the series. Buggy's probably going to end up being the new "King of the World", or it's equivalent. It's just that, much like in Cross Guild, he's probably going to have very little power himself, and he's probably going to get pushed around and abused by everyone else a lot. (Stupid, dead end job.)
Will Buggy also become the King of the Pirates? At least publicly? I'm not sure. I fully expect Luffy to become the "true" King of the Pirates. But, in the eyes of the public, I wonder if Buggy will get that title, too. Like, Buggy stops early, but Big News Morgans captures a key moment on camera of Buggy being on Laugh Tale, or holding Shakky's one-piece swimsuit or something. And Buggy becomes known all throughout the world as the King of the Pirates. Shakky's one-piece swimsuit becoming his new flag, his new symbol of his rule. Turning the joke we've all made into canon. Even though the actual One Piece is something else that Luffy finds in secret.
I could also see Buggy as a "epilogue" villain. Like, we flash forward 10 or 20 years, and the Strawhats all reunite on a island. And Buggy just so happens to be there, and ends up clashing against all of them, one by one, as they show up. Like a repeat of Return to Sabaody.
Or maybe even before that. Maybe Luffy finds the One Piece, fights the True Final Boss, whoever it turns out to be. Everyone's happy and celebrating the big victory...and then Buggy sneaks up and stabs Luffy in the back. Buggy as Saruman taking over the Shire from Lord of the Rings, basically. Buggy threatening their happy ending, not because he's strong, but because he's sneaky and patient. Then Luffy has a fake-out death scene. Because there's no way Oda is ending this on a sad ending.
It's also possible that Buggy could be revealed to have one of the Secret God Fruits. Personally, I doubt it. I think all the God Fruits are better off with different characters. But, it's not impossible that Buggy's Chop Fruit is more special or important than it currently appears. Buggy's Fruit could come into play at a key moment in the finale. The Chop Fruit shares a lot of overlap with the Ope-Ope Fruit, though. So I'm not sure what Buggy could do, even Awakened, that Law couldn't.
I've heard some people speculate that Buggy could be related to the Nefertari Family, due to his blue hair like Vivi. And I wouldn't be surprised if Buggy's lineage is special in some way. Shanks turned out to have a pretty special family line. I'd expect his "brother" Buggy will end up having something, too. I'm not sure if it'll be a connection to the Nefertari or not. But, Buggy will probably be revealed or hinted to have a special bloodline of some kind. Who knows maybe he's actually the rightful "priest" of Uranos, like Momo seems to be for Pluton? Crazier things have happened.
So, yeah. I'm expecting some STUFF with Buggy. A lot of it might happen offscreen. Because, that's kind of where Buggy thrives. But, Oda seems fond of the character. I think Buggy's in for a pretty wild ride.