I think this is a bad change that, in the long run, could drive away a lot of players. I can see the upside, we possibly will have more clean and even races since players have more time to get used to the track/car combinations. But for me personally, the downsides far outweigh that:
1. I play only race C, and I enjoy a lot of tracks that the community dislikes (All Bluemoon variations, Alcsace, BB raceway, Tokyo East Outer Loop), and they come up rarely enough, with the schedule changing weekly, I ll have to wait possibly months for some of the to come up.
2. Same as a lot of the players dislike the above tracks, I really dislike tracks like Suzuka and Nürburgring and wont drive them. That means I am either forced to drive tracks I dislike, or quit Sportmode for a week.
3. Even for my favourite tracks, I wouldnt want to drive them 7 days in a row. The variety is one of the big things that keeps sports mode interesting for me.
IF they want to change to a weekly schedule for good, they need to add more races, possibly one for each class. Or compromise and make them change every 2-3 days.
All of that is of course just my personal opinion, but I am quite disappointed since I made the decision 2 days ago to invest in a wheel setup, and I know with the races changing to weekly, I wont invest near as much time as I planned to into GT when I made that decision.