We expect CentOS Stream 8 to become the platform used to develop oVirt so we expect it to be the most tested on development.
Since CentOS Stream will be upstream to CentOS Linux, CentOS Linux should still be a viable option.
Please note that at oVirt GA time CentOS Linux may be missing some packages or features that should be included in next CentOS Linux so staying on CentOS Linux may mean you'll probably need to wait upgrading to latest oVirt till next CentOS Linux will go GA.
Details about exact flow are still under review.
About Fedora, there's no plan to change our support policy for it, we are going to work with it as usual, trying to support it as best effort / tech preview.
