There are quite a lot o projects which may use PHPUnit via its current API and it would be nice to keep it stable. Codeception is one of them. I'd kindly ask to make all APIs used here https://github.com/Codeception/phpunit-wrapper to be considered as public API.
Also, I know that JetBrains also heavily relies on PHPUnit internals to make their integration working.
Not sure of issues on their side but I think we can invite them for the discussion.