Blizzard's addons *are* loading, but because addons are disabled, they're shown as red in the menu. (You can't actually disable them from there, anyway.)
/script and /run were disabled with last night's patch. People were using macros to run mini-addons, getting around the "addons are disabled" setting. Blizz wants their stuff tested right now. There is still plenty of default UI that needs tested. For example - there was a completely different *new* talent UI before last night's patch.
And the guild interface still doesn't exist on beta because they're completely revising it.