I'm hoping the UI is actually fully customizable and not just movable and hideable. e.g., completely resizable, color changes, and backdrop options.
My problem with the UI is not that it's too much (though it is) but that the lack of a background and the vivid colors used in the displays just vomit all over the gorgeous scenery. Too much contrast and it makes it hard to read. I'd rather have a non-transparent UI backdrop that makes the game look like it's being run in a Windower.
The thing I hate most is all the enemy data. It's important to be able to see the information, but the way they have it ruins the scenery. I hope it's at least down to a keystroke to toggle on/off.
What'd be really cool is a smart UI that can be set up to only display when needed. e.g., your connectivity is only displayed if it dips, ally HP is only displayed if it's low, etc.
A smart UI does sound amazing, but I can answer that the UI is movable and resizable. You can change font colors, sizes, even the font itself I believe. I'm sure with addons you'll be able to change even more like add different borders, backgrounds, etc.