In addition to the three new cars, I predict the following:
-Either a new track layout, or a new venue altogether, complete with at least one new Circuit Experience. The last one was quite disappointing - with a mere changing of where the starting line and pit exit is - but I'm confident that it's all uphill from here. Maybe this time, we'll get the return of Apricot Hill, or an alternate layout for Colorado Springs.
-Either additional rounds for certain events in World Circuits, or new events altogether - or perhaps both. I'm really hoping the supposed events for Gr.1 racers and Hypercars are coming sooner than latter. We definitely need more races at certain venues, too, like Kyoto Driving Park, Monza, and the Sardegna Road Track.
-Possibly another mission pack, complete with two prize cars. (I'm pretty sure the last drag mission has a name that implies it's the first in a series.) Keep in mind these future prize cars could definitely be legendary cars, as we've seen with the Chaparral 2J, the Aston Martin DB5, and the Nissan Fairlady Z (S30) 432.
-Additional QoL updates/bugfixes, including those beyond the officially-acknowledged bug list.
Ideally, I'd also really want to see more menus, as I think there remains tons of potential for other trios of cars, like the pre-release builds that showed menus for kei cars and the Toyota 86. I'd also like to see more championships, especially those that use Gr.2 and Gr.1 cars. These championships would ideally require the later licenses, too.