I see one another very simple way to keep the game somewhat fresh for at least a bit longer: mixed seasonal championships that combine courses from street, road and dirt racing (I’d prefer if PGG kept cross country out of the mix )
As for game’s complexity: this is something I can praise Gran Turismo 7 for when compared to Forza. This game has a very thorough manual that explains every part of the game to newbies.
I liked the idea of explaining how upgrading cars works in FH5 through the Donut Media story but the execution of it was very poor IMHO.
EDIT: I’ve created a suggestion for mixed championships