Looks like we'll not be able to ship a Fedora 12 KDE live spin free of a kde3 runtime after all.
The reality is that the kde4 ports of both k3b and koffice aren't quite ready, and not recommended for use by either upstream. So, our plan is to revert to the tried-n-true k3b-1.0.x and koffice-1.6.x (as in Fedora 11).
Don't fret however, we'll continue to provide unofficial kde4 builds of k3b and koffice in the kde-redhat/unstable repos. Testing and feedback will continue, and with good confidence, we'll be able to include both of these in Fedora 13.