I understand the frustration. I don’t know what the exact wording was on which you relied, but it does remain true that Scrivener 3 is on the way, and you will be able to upgrade when it gets here. But, if you hadn’t been using Scrivener before and were eager for the full cross-platform experience, I can imagine that the delay would be aggravating.
OTOH … L&L does give an indication of the development process in the beta release notes. As for announcing a date and then communicating why it was missed … well, they tried that, and got about the same as what you’re posting here. It may not seem so, but it is actually more responsible for a developer not to announce a release date, because it is of the nature of complex software programming to be, well, complex. A butterfly flaps its wings in line 1123, and a unicorn dies in line 927. Release dates inevitably get postponed; or really inadequate software gets released right on time. Either way generates about the same, or greater, levels of user dissatisfaction as just not announcing. I suppose the smart thing to do would be to announce that the upgrade will be released on Feb. 29, 2024; and then when it comes out almost 4 years early you seem like a superstar.