This is all true -- and a good reason not to be too early an adopter of these new cars. Pretty much any new car will garner a lot of initial attention and the motivations all favor the dealership until the first wave of eager buyers have gotten their cars and demand settles down to a more normal level. Many buyers in that first wave are already sold on the car and are not all that price sensitive. They want the excitement and bragging rights of being among the first to get the car. Dealers hold the winning cards with these customers and may fail to think about what will happen later on, after these customers have gotten their cars and the next round of sales will require somewhat less enthusiastic buyers.
How the dealership treats people expressing interest during that first wave of interest may well determine whether they come back after demand subsides. Plenty of people making inquiries early on may not be ready to buy right then and there but may well consider a purchase a bit later on, after they've gathered more comparative information. If customers are put off when demand is high, they may look elsewhere once they're finally ready to purchase, when the dealership no longer has people waiting in line for a car. Courtesy and honesty are the foundation of a good customer relationship and treating customers contemptuously or inconsiderately merely because "they can," isn't in the log-term interest of a sales person, a dealership, or a brand. Why not simply explain to people that cars aren't available at present for test driving due to their very limited supply? This should be done with an apology, not with condescension. I've had dealers of other cars tell me that they didn't have cars in stock but would ask a customer if they would be willing to have me drive their car while it was in for service or before delivery. The understanding was that, if the customer agreed, the test drive would be a bit gentler with the goal of giving me a feel for the car but not testing its full performance capabilities. They also made it clear that customers may be reluctant and decline. If all parties have a good sense of trust in the sales person, this can work. Even if this sort of test drive isn't a possibility, a sales person can explain truthfully and respectfully why a test drive isn't an option at present. I've dealt with sales people who have taken this honest, considerate approach and ones who haven't. The former are far more likely to get my business.
Hopefully, Genesis won't make the same mistake as Kia seems to have made. Potential customers are a dealership's life blood and even if they can't be converted to a purchase immediately, their good will should be cultivated, not squandered. This is especially true in the premium segment that Genesis aspires to and, presumably, is a substantial part of their decision to have stand-alone dealerships for the Genesis brand.