GlassJoe pretty much took the words right out of my mouth. That's exactly what I was thinking last night. The game has been out for almost a week now. At this point, someone would have found a Brutality and it would be all over the place. We're in an entirely different generation now than we were 15 years ago. Like I had posted earlier, Brutalities were something that were discovered by accident for a lot of people on UMK3 console versions. These days, with people playing so fanatically and hacking games the moment they come out, they would've already been discovered within hours of release. I'd heard of people who went to the midnight release of Mass Effect 2 beating the game in less than a day (considering it's a 35+ hour game, that's quite a feat). Something like MK, which can easily be conquered entirely in one day with every mode completed, something would've been revealed by now. Heck, Babalities were only a secret for a few hours.
I'd like to hold out hope that there's some unique way to do them that we haven't discovered yet, but much like the "multiple variations of stage fatalities" and the stage fatalities in the Wasteland, Bell Tower, Pit Bottom and Goro's Lair, we're on a fool's errand looking for something that doesn't exist.
However, the recent news article that NRS will be secretly applying updates to the game definitely supports the theory that they may be added over time. I actually like this tactic from NRS...keeps the game new when you least expect it.