There's gotta be something we don't know about... something involving the dynamic between SMI at the Fairgrounds and Dover at the Superspeedway. When the Superspeedway race was announced, it was said to be potentially beneficial to the Fairgrounds. But how? I've never understood that.
As mentioned by
@Spotter22, the Superspeedway has a 4-year sanction agreement, and will be making significant capital expenditures to make the venue Cup-ready. If the race is passably successful, that would seem to preclude NASCAR doing anything at the Fairgrounds... unless there is some undisclosed situation that would enable SMI to ride into town and replace the Dover group in Nashville.
I predict SMI buying the assets of the Dover group. They may have an option or something already... although I'd think a public company would have to announce such a thing...?