One thing I'd love to see there is a consistent use of the Arquillian container profile, or even have a strong recommendation Arquillian is used.
Additionally, though I'm not in any way a fan, all of MP (if I'm not mistaken) as well of CDI, BeanValidation and Batch use TestNG, not Junit. Perhaps it's best to have some consistency there as well.
I remember that in Java EE 7 samples we had the door open for "whatever" and essentially every test used another combination of technologies. The permutations must have been a dozen or more.
As test engineer it's not unlikely you have to jump between tests for different but related APIs., E.g. for Jakarta Faces I'd jump between Jakarta Servlet, Jakarta _expression_ Language, Jakarta WebSocket, and Jakarta Security. Having to adjust mindset every time would not be productive, especially since often there's no reason for a project to use technology X over technology Y other than that person A just started to use X and not Y.
As for the Arquillian and consistent use of profiles; as a Jakarta EE vendor I'd hate to write and maintain adapters and porting kits for every API in Jakarta EE. Ideally I provide 1 implementation to run all of the APIs that make up the full platform.