Now that I think about it, I'm pretty sure the promotional art per se is only secondary to the real issue. I don't think I'm wrong when I say that FemShep always felt a little... less graphically crisp, than the default male Shepard. And then there was the whole issue with the vote on her looks, and how she did not look all that much like her cover art in the actual game.
If they choose to use the female protagonist in the cover or in trailers I hope they'll keep that in mind. Frankly, I hope they have worked harder at making non-default Shepards in general look better. It was really hard to customize him/her and end up with something that looked nearly as good (graphically speaking) as the standard MaleShep.
I remember firing up ME3 again after Mark Meer signed my promo art at Comic Con. I looked at that Shep, then looked at the default. Looked back up and then looked back at my monitor. I started laughing, because the disconnect between promo art and the in-game model was extremely bad. I'm thankful I'm on PC and I've got mods that actually make her look much closer to that. Aside from the default from ME3, I thought she looked okay except for in ME2. Not sure what happened there but I agree that it didn't look as good as Sheploo. I felt the DA:I team did a much better job of that. Those presets look pretty good. Except for the sideburns on the female character, but a different rant for a different thread.
With that fan vote, I couldn't stop shaking my head when I found that out. I don't care if it's a male, female or polka-dotted character, the designers should do it without fan input. My "favorite" part of that is folks crying that it was sexist that the blonde hair/blue eyed Shep won.

Seriously? I don't know what's worse. The fact that BW thought it was a good idea to let fans vote on FemShep, or the fans that thought it was sexist and "conforming to the typical straight white male ideal," over a frigging hair color.
Pro-tip: If you want to be taken seriously in regards to female representation in video games, pick your battles. Don't start accusing game companies of being sexist over hair colors. That's a great way to have a bunch of people pick anyone up that is promoting gender equality and feminism and throw them into the crazy pile. Seriously, cool down your jets.
I wanted to mention avoiding the "default" look is another reason why I'm kinda meh on the whole idea on having any obvious gender on the cover. I'd like to see a focus on say, a real world picture of Andromeda and the logo for the posters/cover art. To me, that's my symbol of the game. Just like the Eye of Tyr from NWN or the blood dragon logo for DA. The PC is secondary to me in the cover art and posters. I do believe in equality between genders and I've definitely gotten my share of flack for it. I've just seen firsthand what's more effective these days. Trailers and convention videos are actually more important to me at this point. I'm willing to bet that a lot of gamers are more likely to check out con footage over the actual trailer.