I think bioware must allow using interface addons, like Curse.com site. Healer, tank addons.
Though we don't have any news about allowing third-party interface addons, we'd definitely be interested to hear what functionality you feel is important to add to the current UI. Others have offered a few suggestions (thanks!), and it's helpful to us if you describe what you think is missing and let us know what we can do to improve the UI!