alt Hacker NewsWP Engine could legally do this, but if they had the development resources to do so, Matt Mullenweg probably wouldn't be doing legally questionable and morally reprehensible things to try and coerce WP Engine into funding WordPress itself. Maintaining a fork of WordPress with its own independent development priorities would involve a lot of work.
What WP Engine will most likely do is run their own plugin repository mirror, strip off whatever trademarks they don't feel legally empowered in using, and move on. WordPress cannot legally exclude WP Engine from using WordPress code.
> Maintaining a fork of WordPress with its own independent development priorities would involve a lot of work.
What if they had no interest in developing new features, and just concentrated on security and bug fixes for the current version?
I'd expect that most of the people who use a site like WP Engine to host their WP sites want to put out their content in a nice format and once they are happy with the way it looks and the tools they have for editing and administering it they would be would be fine with it staying on the same WP feature set for many years.