Yeah, I'm thinking that might be their plan. Have this one single Forza Motorsport game, updated with DLC for the rest of the generation, much like Halo Infinite is planned to be the only Halo this generation with DLC support for the whole gen.
With the bethesda acquisition and hopefully one or two more, we'll have a steady amount of continued content coming in that we won't just need Halo, Forza, and Gears. Giving them more time to perfect their games, add single and MP content as well. Maybe even Phil will let them (Coaltion, 343, and Turn 10 work on new projects lol I know, not gonna happen, but I can hope).