There seems to be quite a bit of discussion about RHEL 6 lately (see latest issue of DistroWatch Weekly).
From the Red Hat employees I've talked to, it appears that RHEL 6 will be based on Fedora 12 and have a 2.6.32 kernel. There have already been a couple of Red Hat internal RHEL 6 alpha releases. Hopefully a beta release of RHEL 6 will be available in the not too distant future. Expect the GA version to hit sometime this summer.
So far as Red Hat not announcing things way in advance... that's just how they are.