It's brand new, and called "Metro". Wait, we changed our minds, it's now called "Windows 8 Style Gui". Oops, strike that. Seeing as how it will be released tomorrow, today seems like the best time to start calling it "(New) WIndows User Interface". We like it, because it's bland and unoriginal.
Give us a week, and we'll call it "Super Windows 8 Start Menu". That way, we can laugh at the people who accuse us of removing that Start Menu from 8. After all, it we'll be calling it a Start Menu, won't we? And best of all, It has an "8" in it, so that will make people think about (and buy) Windows 8.
Then, when we receive a public backlash (as people will refuse to call it a "Start Menu"), we might change it again. Or we might not.