P will not be the mass market car generating most orders. Spreadsheet indicates P to be about 11% of overall orders after 6/27 and that excludes all SR demand still waiting, so the real number for P could be between 5-8% of all orders.
I don't see how P test drives would change orders dynamics dramatically. I have my order in, but if I was a new customer considering Tesla for the first time and I just had a test drive, I would think "ok, this car is fast, but its out of reach for me financially. And those I can afford could be significantly slower/worse (nobody saw non-PUP yet)...I probably need to wait to see the equivalent of a car I can afford..." The way those P cars could be helpful is to validate whether the inside space is adequate, they didn't need to be P for that though. I think having RWD/AWD available for test drives instead of P could be more helpful.