Agreed. I do believe that for most IPs, it's good to look back, and specifically examine both what did and didn't work, and pick what features still have potential to evolve. For example, I think the territory mechanic from Carbon has a ton of potential to become a multiplayer feature that would promote a self-sustaining ecosystem of emergent gameplay. I also really liked the reward card mechanic, FWIW.
But yeah, I could see the territory mechanic being revived, where it'd keep the concept of there being three or four teams, and each one would have multiple sub-teams that fit the "major" team's motif. Idk if the various motifs in Carbon would be best, though - I'd likely keep some while replacing others. It'd also depend on the cars available. I could see a team that has a motif of using cars that've been homologated into FIA GT3 cars in real life, for one idea. So that'd mean cars like the 458, the Huracan, the GT-R R35, 12C & 650S, and so on. If a player gets bored of a team, they could switch (both between sub-teams and major teams), but there could be incentives if one of these teams has a disproportionately low amount of players, such as credits bonus if you win an event while driving with that team. It'd be made so that you're not locked into a team, but players are encouraged to keep the population of each sub-team (and thus, major team) relatively balanced.