Summary - we don't want to diverge from upstream on this feature. For the reasons Jeremy outlined - mainly that it's an important feature of Shell's branding. Since the bug was filed we've themed Shell and added extensions to the default Ubuntu session, so there is (IMO) sufficient branding to satisfy these concerns.
We just talked about this at a Desktop sprint.
Summary - we don't want to diverge from upstream on this feature. For the reasons Jeremy outlined - mainly that it's an important feature of Shell's branding. Since the bug was filed we've themed Shell and added extensions to the default Ubuntu session, so there is (IMO) sufficient branding to satisfy these concerns.