If you've played a modern MMO -- which I'm just about certain I recall you having done -- you'll know exactly what the HUD needs to be. The default should have sufficient information that the player can play the game, but the rest should be entirely the choice of the player -- maybe not to the point of including in game scripting and macro-capabilities and such, but everything else f'sho.
It should be easy as pie to remove an element from the main bar, move it to a different part of the screen and pin it there, resize it, add other stuff to the main bar, make some HUD elements transparent, move the main bar to the side or top or even middle of the screen, and just generally change EVERYTHING.
Everyone does things differently -- the only thing we can all agree on is that we'd like the freedom to do things the way we want to do them.
Will this sort of flexibility be a big sales winner? Probably not. Will it be a huge deal for most fans? Probably not. Would it seriously please a certain segment of players? Almost certainly.