Two questions pop into my mind: A. How easy will it be for the unlucky people that have installed Centos 8 to convert it to rocky Linux? B. Will rocky Linux fulfill its promises? I mean if I install rocky Linux 8.4 will I still have a supported OS at 2029?
I'm not sure that's a fair question to a new project. If you asked that recently about Windows 10, you'd have a different answer than today.
But seriously, Rocky was started by the person doing CentOS before and unhappy with changes. They're at the very least not planning to go away.