For cars, I predict four cars as being the most likely quantity. As to what they could be, I have no clue. I also predict there'll be some sort of event for GT7's first anniversary, very much like the GTWS '22 World Final last year, where we had a series of Daily Races where we won a lot more credits.
I think we're very much overdue for a new set of missions, too, but I don't think they'll be the 24h races that were mentioned at some point. Instead, I think they'll feature some of the new cars/tracks that've been added since The Human Comedy, especially since the final drag mission implies there's more to come. Who knows, maybe we'll also get a set of missions based on hillclimbs, with ideally both Pikes Peak and the Goodwood hillclimbs appearing in GT7.
I also imagine we could use another Bonus Menu or two, maybe even three. But this time, I think we could see new championships instead of just a new trio of single races. This would especially be nice if said championships required some of the later licenses, or more advanced cars like those in Gr.2. I could see another Bonus Menu championship featuring the F1500T-A at various circuits that've been part of the actual F1 calendar, such as Brands Hatch, the Nurburgring GP course, and Fuji.
As for any Extra Menus, I bet the next one or two that we get will continue the trend of including at least one car that's part of the update. I, for one, am surprised we still don't have Extra Menus themed around McLaren, Aston Martin, or Lamborghini. An Extra Menu focused on the various V12 Lamborghini models would seem obvious, considering we've had Extra Menus focused on mid-engined Porsche models and inline-six BMWs. Said Extra Menu could feature the Miura prototype (though I'd ideally want to see the Miura SV get added), the Murcielago, and one of the two Aventador models we have at the moment. The reward could be a V12 Lamborghini model that isn't part of the Extra Menu, such as the Countach LP400. (But if it were up to me, I'd add that iconic racing Diablo that was in the JGTC, and then make that car the prize.)
For courses, I think we could see a new Grand Valley layout coming, as well as one for Colorado Springs. But I also think we're overdue for a new Asia/Oceania circuit, so maybe a hypothetical West and/or North layout for Tokyo Expressway could be coming. The return of Twin Ring Motegi would be fantastic, though, as would the potential debut of another Oceania circuit like Phillip Island.
Finally, for engine swaps, I'd like to see something for the older Fiat 500, given how the Abarth 595, Volkswagen Beetle 1200, and Mini Cooper S '65 all have obtained engine swaps. I'd also predict a new car that can get the Lamborghini Aventador SV engine - possibly the Miura Prototype - and possibly the Escudo engine. For that last one, I'd expect it to go into one (or both) of the two Swift models. I also had a second LS9 and already put the first one into a Trans-Am, so maybe it could go into some other classic muscle car, like the Corvette C2.