You can trick it into installing by changing SystemVersion.plist but it's a dirty hack. Xcode did seem to launch fine though afterwards (I only used it to activate Developer mode on my iPad)
Wow, check out the removal steps in the kb article. Quit the app using Activity Monitor then delete from /Applications. Clearly we have a long way to go...
That's not true, Applications could still run as root but be signed and subject to approval as they are now. The only difference I can think of is they just wouldn't be sandboxed any longer.
Will it be maintainable? What happens when there's a collision and we have a pile of milk and rotting eggs stuck in the most inconvenient place possible?