I sincerely doubt they're going to make this change. They're already probably spent the better part of a year designing and modeling them. The reason they probably have elezen proportions (and the female have miqo'te proportions) probably has a LOT to do with modeling all of the armor in the game.
Here's something to think about: There will never, ever be a race that deviates too far from the proportions of the 5 races we have now. To do so would mean remapping and remodeling every single piece of armor in the game. And the development team has mentioned time and time again in QA posts that getting the armor we have to work correctly is already difficult. They're going to take shortcuts whenever possible.
And the Au'Ra in the official art looks like he has shoulder pads for shoulders. I'm not seeing any significant differences that wouldn't make him look silly.