I think we'll get at least one more year of updates for GT7, and by 2028, things start to slow down a bit before any indication of GT8.
By the end of this year, we'll likely hit the high 580s or low 590s in terms of car count (not including Power Pack cars or any bonus cars), and it's possible that by the end of 2027, we'd be somewhere around 620+ cars, roughly 200 cars added since launch.
That's also slightly more than the Japanese version of GT2 which had 604 cars.
As for tracks, maybe around 43-45 track environments at most. Looking into the future, it's inevitable that GT8 would be an absolute beast of a game in terms of its car and track roster.
Makes you think that GT7 is a game that's built to last. I sometimes rewatch the announcement trailer, pre-release trailers and past update trailers to see how far we've come.