I just pushed a set of changes to the desktop-effects repository on fedorahosted to add support for GNOME Shell.
The basic idea can be seen in the screenshot attached - instead of a single "Enable Desktop Effects" button, the user is now presented with a three-way choice of "Standard" "Compiz" and "GNOME Shell", with short explanations for each. As before the choice is instant-apply and when the user is switching to a compositor, they are presented with a count-down dialog that they have to click on to confirm their choice.
UI suggestions, small and large, appreciated.
The dialog will be split out of the compiz-gnome package into a separate package required by both compiz-gnome and gnome-shell.
If compiz-gnome or gnome-shell is not installed the option is simply not shown. It would be neat to instead have a "Not installed. _Install Now_" message with a package-kit enabled link, but:
A) I'd have to implement it
B) I'm not completely sure that we want to make it quite that easy to try out GNOME Shell with out any context. If people have to read about it somewhere and install gnome-shell as a separate step, then they'll have the opportunity to get some context.
C) I'd have to implement it
Longer-term, maybe even in Fedora 13, the idea is that desktop-effects goes away. Switching between gnome-panel/metacity and gnome-shell will be done through standard GNOME dialogs, for as long as gnome-panel is still supported. gnome-shell won't have the inter-distribution differences that made a unified switcher to Compiz impossible.
For Compiz, Fedora should stop using the GConf plugin and ship a Compiz that is more natively "Compiz" and uses the standard Compiz configuration tools. Presumably those tools already provide the opportunity to switch your session to use Compiz, if it is not currently running, or will do so in the future.
- Owen