Its more like the restrictions in prologue, but i really have no idea about the track day things... Yet
Right, but GT5P did not restrict you from any race as long as you had the car. What I'm assuming is that PD will separate lobbies for different A-Spec levels, for example, 0-10, 10-20, 20-30, 30-40, 40-50 etc. I'm making these levels up. And within each lobby, cars will also be restricted like you can only drive low powered cars + karts in 0-10, some supercars in 10-20, most supercars + low powered rally in 20-30, SuperGT, DTM, Nascar, rest of Rally in 30-40, and finishing it up with Group C, LMP, F1, X1 in 40-50. Again, only assumptions.
But with this system, we can be assured that people who step into the more powerful cars have some skill in controlling the car. As much as PD can't 100% prevent punters, this system will force noob punters to stay in lower levels and never reach higher powerful cars unless they learn how to drive properly. Obviously, there will still be a few high level punters who like to muck around, it'll have a less impact on higher level racing.