I don't think there's any GUI way to switch between say Xen and non-Xen kernels
by default, nor is there any GUI way to tell the installer whether to change the
default kernel on upgrades. I believe system-config-boot is the ideal tool for
such settings, in a separate Advanced screen.
harald isn't most of this implemented in one way or another now?
no, it isn't
Even if we do not add additional GUI to system-config-boot, it should be changed to set UPDATEDEFAULT=yes (in /etc/sysconfig/kernel) when changing to a Fedora kernel from a non-Fedora one, and
UPDATEDEFAULT=no when changing to a non-Fedora kernel (such as Windows). See Bug 498689.