I think it would be a good idea to change the cars available in the yellowbird and skyline nismo trials. Switch them out periodically, maybe once a month or even every update. It wouldn't be game changing but it would give players a chance to "buy" low end cars with renown. Make them all different individually like the singleplayer prize boards.
#Singleplayer trials replay prizes
scenic venture
tiny hazel
I think once a month is probably too much work for hutch, but to refresh them every time there is a car update is a reasonable request.
And I'd restrict the cats that rotate to just the 20 levels that cost 300 renown.
rare portal
There are 110 different SR and 116 different rare cars in the trials. If these cars were to rotate again and again, players would have all SR and rare cars in their garage by the 7th rotation at the latest. There are only 20 URs, but I think it's even worse if players can get their missing URs via the trials. The exciting thing is that everyone has a different garage. I don't like this idea at all.