I think you underestimate the logistical challenge of shuffling a bunch of super-early production vehicles to every corner of the country to be beaten on as demo models. Particularly for something that history shows the great majority of early purchasers just don't care about.
2 years ago, I purchased an Audi A3 sedan. new platform, chassis, etc, started from scratch.
Audi was able to cobble together demo cars for their showrooms to host test drive events in April, before the 1st deliveries began in late May.
and those cars were not on trains....well, some were, after their boat ride from Germany, via Gyor, Hungary.
so yes, sometimes vehicles can be scratched together for test drives.
I mean, just six weeks ago, we saw drive-able prototypes in Hawthorne....come to find out, those may have been Betas, as the design might be finalized in just another 6 weeks.
Unless your name is Elon Musk, I'd probably hold off on saying something can't or won't be done at this point.
FWIW, I do think a majority of Model 3 reservation holders would love to have a test drive before configuring or taking delivery. I know I would.
but I'll still complete the transaction without one.