Okay, I feel like I should share my thoughts here, since lately I've been browsing the blogs regarding what people wish to see in Update 10 (because I'm interested too) and it's really cool to see some people's ideas here because some of them are really fresh and interesting. However, I'm also seeing more of this specific gripe popping up in the comments about toggling the genders of your Warframes, because apparently this is such a big deal that they're getting really heated about it and it's a bit worrysome, due to in no small part the fact that these people are probably missing out on some very fun frames because it doesn't happen to be the same gender they are in reality.
To an extent, I can kinda understand why: it breaks the illusion, especially when you're putting yourself in your favorite Warframe's shoes and doing a little roleplaying. I have nothing against that. At all. If that's your thing, go for it and have fun. But if you're a dude or chick and you're feeling squeamish at the thought of playing a Warframe because it happens to be shaped like the opposite sex, let me tell you right now, you've got nothing to worry about. Why? Because a Warframe isn't just a suit your "character" wears in the fray.
Each Warframe is an entirely separate character. And I can show some evidence to back it up.
In Livestream #9, at about 14 minutes in, we see that the team has created custom idle animations for each frame (hopefully to be implemented soon). Go on, watch it. I'll wait.
See how each frame carries itself differently when standing still? This is to show off its individual personality, something that could not possibly exist if you just "change what suit" you're wearing when you select a frame. If that were the case (and, regrettably, it is at the time of writing), then all of the idle animations would remain the same and the DE team would have no plans to change it. But they do plan to change it, as evidenced by the fact they've already put the work in for it.
I hope that explains things well enough, but I'll sum it up one more time: if you're put off by the fact that you'd be playing a Warframe of a different gender because you feel it would be "crossdressing," remember that you're not just swapping what you're wearing. You're actually choosing to play an entirely different character that just happens to be male or female.
Now stop denying yourself some fun. You see that Ancient Disruptor? He needs his face burnt the hell off. With fire.
EDITED 07/31/2013 - Hoo boy. I didn't realize this was going to get as big and ugly as it apparently did. My objective here wasn't to try to force my opinion or be disrespectful (as I made it a point to avoid seeming accusatory); on the contrary, I'll support whatever decision DE decides to go with regarding the game/character design. I was merely trying to explain away a problem that a very niche group of people had with the game, in the hopes of helping them have more fun. I like having tons of options just as much as the next guy: I was stoked to see more helmets added and I hope to see more additions and skins later, for example. So, if they make changable genders, that's cool, but DE's been pretty clear on the stance they take regarding this issue and I wouldn't expect them to change it anytime soon. If it continues to bother people...well, then I guess they'll just have to either live with the choices they've made and have as much fun as they let themselves have, or change how they see things and, well, introduce themselves to the options they wouldn't let themselves have before.
The game's there. Play it how you want. Just remember that nothing's closed off to you except the doors you choose to keep shut. I hope that puts it in a better perspective.