Hi,
It's been a while since I was on the user side of the fence but it's hard for me to imagine companies would want to migrate to Jakarta EE 9 just for a namespace change from javax. to jakarta. (I think someone else made this point but I agree).
If I was in charge of a large system (I actually do have experience although very, very dated) I would not change to a new app server just for a namespace change. There would have to be a compelling and dramatic improvement in the platform for me to want to move at all. Something I cannot get with the existing platform. Switching without a really strong business case is irresponsible and I don't see a namespace change as a compelling business case for end-user companies.
If Jakarta EE 9 is just a continuation of Java EE with a new namespace, then seems to me that we are giving up a huge opportunity for Jakarta to become something better. We can take all that we've learned over the last 20 years and without the baggage of the past move forward with a truly modern platform.
I would not even release a Jakarta EE 8. Instead, I would release a Jakarta EE 8 Legacy Profile that will never evolve and will remain separate from the rest of Jakarta EE