You shouldn't just assume that GT7 will be out (and that it's round the corner). Assuming makes an ASS out of U and ME. Yes there is strong likelihood that there will be another GT title but it depend on which kind of game it will be? GT Sport I would say has been quite a success, so another go with sport isn't a bad idea.
Yamauchi already said what kind of game GT7 will be : "Next Gran Turismo Will be a ‘Combination of Past, Present, and Future’"
https://www.gtplanet.net/next-gran-turismo-will-be-a-combination-of-past-present-and-future/
So nothing to worry about race cars, esport, all kind of cars, campaign mode and more