Depending on which jurisdiction you are in, absolutely.
It could constitute bait advertising. The practice of using fake advertisements to get customers into your store for the purpose of trying to sell them something else.
Possibly, but per [1] it would come down to: "(1) whether the practice injures consumers; (2) whether it violates established public policy; (3) whether it is unethical or unscrupulous."
e.g. it might be deemed "unfair" if you're promoting vaporware to try to slow down sales of a competitor's actual product, and someone could prove consumers suffered "substantial" injury by holding off on purchasing something useful while waiting indefinitely for something else that you had no intention to actually sell. (Proving this would be hard, but I'm sure it's possible.) On the other hand, advertising a joke product—where a reasonable consumer is unharmed because they should have known it's a joke—is almost certainly legal.
