It's not a technical limitation of the engine or something, like that older post seems to imply. (And that's likely an incorrect interpretation of the original answer provided back in a live letter or something).
The "game breaking" issue is that if SE adds more faces, they'd have to go re-QA all the animations to ensure it doesn't clip or animate improperly, and as seen with how they've handled newer race additions, that doesn't seem to be a priority. Adding in more faces without doing the proper work for it would just result in first-party "modbeast" issues otherwise, which would be divisive.
I'd definitely like for them to add more options, especially since the "graphics update" is exactly the sort of opportunity do this sort of work, but I'm not hopeful. It's still weird that /new/ hats are barred from Viera and Hrothgar. And that only midlanders have 6 faces, which is still not diverse enough, but a major step up from the 4 for every other race/clan combination.
