It is indeed just 6 cars all with different colored alternates. And of those six, they only represent 2 manufacturers (Chevy and Toyota) and three teams (Stewart-Haas, Joe Gibbs, and Hendrick).
I have a feeling the "NASCAR license" may not be a full one, and instead come on a track by track and team by team basis.
If they do add other NASCAR tracks, I have a feeling they're all be ISC-owned circuits (California, Chicagoland, Darlington, Daytona, Homestead-Miami, Kansas, Martinsville, Michigan, Phoenix, Richmond, Route 66, Talladega, and Watkins Glen). California and Homestead-Miami would at least be useful for their infield road courses, and Watkins Glen could be a big bonus.