Well, PD is guaranteed to try adding as much cars as possible, and previously, PD was also slow in giving other features too, like making the game actually complete in release or completing the game with later updates, where the time PD added some features, other developments would have pumped up a new game... So how many car counts, IMO, can also be used to judge how fast PD works currently for the game's other features, how complete the game will be, like adding more tracks, etc.
The thing is I know that it takes work to fully model a car, but there's a faster way to do it like, PD having enough number of employees (it's a small company, only under than 200 employees, while Turn 10 has more than 400 iirc last I know, and big companies have thousands), with the asset they have it should be easier to accomplish the manpower. I heard that PD has opened a new studio, to focus on GT7. Also, they can outsource instead of doing anything at home, which PD reportedly has done by the time of GTS, but dunno when.