I'm sure the mask will be great for the type of person who, when the play the Elder Scrolls, makes one character who joins the Thieves Guild, the Mage's Guild, the Fighters Guild, The Dark Brotherhood, and any other faction they can find. (Complaining online about how dumb it is that they can join every guild is optional.)
Speaking just for myself, I am not that kind of person. If I want to join 4 factions which all have mutually exclusive philosophies and favoured skills, I make four different characters, one at a time.
So for me, if I have a D:OS 2 party of 4 characters picked out, I'll just try to play the game with those 4 characters, and I don't mind if not using the mask means 'missing content' on that playthrough.
The people who are complaining do have a point, though. Being mutually exclusive gives weight and meaning to your choices for this particular thing. That is what choices are about, aren't they? If you could do everything you want, whenever you want with no consequences then that's not a choice, it's a sandbox with no structure. You might argue that this gives us more freedom, but it detracts from the seriousness and integrity of the game. Its game-y-ness and artificiality are brought to the forefront and it breaks any kind of suspension of disbelief. Everything around you should react naturally and logically to your actions and choices, otherwise we get the ME2 problem of having no connection between the choices and outcomes, like the loyalty missions dictating if somebody will die at the suicide mission, but that doesn't make any sense, because the two are not connected in any way.
The shapeshifting mask worries me a bit, because it threatens to make your origin choices obsolete. If it's only given on a second playthrough and is not forced into your inventory then I'm going to be fine with it. Besides, seeing all the content in a single playthrough doesn't befit a serious RPG :p
