This is the most ridiculous claim the "researchers" made.

The control opcodes and registers the researchers found were neither meant to be inaccessible nor left in by mistake. They were just undocumented, because Espressif expects integrators to use the provided protocol stacks. Building half of a radio in software is Chad-level engineering, presents numerous challenges for certification, and would be a nightmare to provide tech support for. Nobody bothered reverse-engineering the provided protocol stacks because it's a difficult task that only leads to harder challenges.

Undocumented opcodes and registers are extremely common. A company may have special diagnostic commands used at the factory to validate chips that they don't share with their customers. Qualcomm has peripherals on its CPUs that it doesn't document the interfaces for and expects integrators to use the provided drivers. Or maybe a command was too buggy so it was erased from the documentation and never disclosed.

I call this the "sales attitude". When someone is just a salesman and not a businessman, they tend to think "How much money am I making at this moment?" and not "How much money will I make in the long term?" This kind of thinking does not work for running a business. They have boosted profits since the last big dip in the early 80's, but in the process they have run the entire record industry into the ground. Everything is over-valued from concert tickets to recording equiptment and an adjustment is in the works.
Companies like M-Audio are leading the pack getting equiptment prices down. The internet is driving down the cost of distribution. Artists are getting rid of the middlemen and hopefully, when all is said and done, we will no longer have people making millions for saying "Uuuuuuuh" over and over again.