Keep in mind that there are fc6-version packages in f7. Lots of them.
Regarding kde, etc. problems, try groupinstalling the kde group and other groups of interest:
# yum grouplist
# yum groupinstall "KDE (K Desktop Environment"
Since the upgrade had problems, then it's also a good idea to groupinstall the basic components:
# yum groupinstall base core
If you continue to have dependency problems, then install yum-utils and use the package-cleanup utility to identify the problems:
# package-cleanup --problems
# package-cleanup --orphans
The simplest way to resolve these problems is to first attempt to upgrade the packages one-at-a-time using yum and then, after that fails, to remove and then reinstall the identified packages one-at-a-time, but be very careful not to uninstall critical packages in the process. It can be very difficult to fix that kind of mistake.
You can manually work through the remaining problems by downloading the current f7 packages that have issues using yumdownloader and then "upgrading" them using rpm. Create a folder to work in and cd to that folder. Pick a problem package and "yumdownloader <package_name>", which downloads the latest f7 version of the package to the folder.
Then "rpm --test -Uvh --oldpackage *.rpm" to obtain a list of missing dependencies. The --oldpackage is used in case an installed package has a later version number than the f7 package currently available. Use yumdownloader to get the missing dependencies and repeat the --test until all dependencies are resolved. Then, "rpm -Uvh --oldpackage *.rpm" to upgrade/downgrade the appropriate packages.
If you hit one that you cannot resolve, then move on to another problem package and come back later to try it again.