I am against this idea. I hate to echo the point, but if one is offended by a game, then one should simply not play it. Now, I mean no offense to the OP. He's not calling for censorship, just asking for a filter. I do not, however, believe that resources should be, in my opinion, wasted on such a thing. Any time spent on a filter to make an M rated game more "acceptable" to other audiences who may or may not be old enough to be playing said game in this first place is a waste. That is time that could be spent on fixing bugs, working out game features, making the net code for multiplayer better than it was in ME3, or, of course, making an ending to the game that won't make long time fans rip their own hair out in rage and disgust.
That being said, I do not mean to imply that everyone who wants a filter is someone underage. There are likely adults who want such a thing too. Regardless, I maintain that such a thing is a blatant waste of resources. Again, if you find a piece of media offensive, then do not consume it. Your particular worldview being somehow violated by someone's work is not cause for censorship, nor even the diversion of resources. I believe that Bioware can make a great game, but not if their time is wasted on things like this.
"Oh, these pacifists are offended by blood. Let's make a filter so we don't bother them!"
"Oh, no, feminists are offended by sex! Let's spend time and money making a filter for that."
"Oh, no! Christian conservatives don't like the interspecies/homosexual sex! Better make a filter."
"Ok, guys, our deadline is here. What do we have done?"
"Well, we have filters to ensure that no one is offended by anything, ever."
"What about gameplay?"
"Buggy as hell. Never had time to fix it."
"What about plot?"
"Unfinished. Had to make filters first."
Coming soon to a galaxy near you, Mass Effect:Hugbox!
Again, I mean no derision to the OP, I simply want to make the point that filters take important time away from the development of other, far more important things. Someone made a point about the profanity filter on Brutal Legend. Recall, if you will, how that game had two acts where it should have had three. Recall also how a sequel was cancelled. I'm not saying a filter kille dthat game, but it was time wasted on something pointless.
In conclusion, the harsh truth is, if one does not like a piece of media, one should not consume it. Asking to censor it or getting devs to waste time on a filter for it to avoid offending anybody is rather selfish and take money resources away from making the best experience possible for people who can deal with it.