Think this might have something to do with the overwhelming majority of the demographic interested in Fallout (and gaming in general) are male?
You seem to make a couple of really strange assumptions. That Bethesda is trying to hide the female lead, that gamers would be offended at seeing a female lead, and that it's not deliberate.
I don't think Bethesda's is tring to muffle anything under a rug, they are however very protective to not spoil anything and do not want to put in the effort on making all kinds of trailers that detract time from working on the game. Pete Hines said that last part.
Gamers play anything, all the time. Male protagonists, italian plumbers in a catsuit, giant blue hedgehog, antrapomorphic mushroom, a literal line. That anyone could possibly think that that showing a female lead would upset these people is beyond me?
Ow and i believe it is very deliberate how they put the trailer together. It showed a clear intent and even a sort of story, or "thread" that ran through it. It was clearly put together very meticulously.
As i said a few posts back it's common practise to market or showcase products casting someone that is of the same six as the largest demographic buying your product. This is not only true in videogames but even more so in other products, i used yogurt as an example. I cannot remember the last time i saw a commercial for some that didn't feature a woman. You think i'm making this up? I'm not the only one that has noticed! Just hit up google. 
So would you say yogurt being marketed predominantly to women and promimently featuring women is also a gender issue? Because to me it just seems like marketing 101.
But as i also said, and im starting to feel like a broken record but ill say it again anyway, female gamers don't care. Mass Effect 3 was touted earlier as an example of how to represent males and females equally in marketing, and as discussed Mass Effect had about a 20% female playerbase.
And yet Skyrim, which only did trailers and gameplay with typical Iron Armor Skyrimdude saw that 30% of it's players were female. Despite doing no "gender equal" marketing whatsoever. Because gamers don't care, not male gamers, not female gamers. Because gamers choose gameplay.
Another surprising revelation from Gearbox from back in 2011, apparently Duke Nukem Forever had a surprisingly high popularity with female gamers. Go figure.