This Natural Motion stuff is quite cool. If you want to check out some videos of it, dig up the Indiana Jones game on IGN's Xbox 360 section. Very nice stuff. I actually downloaded a demo of their old engine to play around with, and I can say despite having a CS degree it was a bit over my head
That being said, this engine would be a huge win for the 2k people because it would actually cut down on the dev time. Madden boasts non-stop of all the motion capture they do...this is UNLIMITED in the amounts of movements they'd see. Granted, it isn't free and would probably take 1000s of man hours to get the parameters of the engine just so, but oh man would it ever be awesome to see it in use.
As others have said, we'll never see it in Madden because they'd have to scrap core code that I bet has been in place since the original madden on the PSX.
Just at work today we were talking about the possibility of creating a game with this engine without a license. We decided the only way this would really, truly succed is if you were able to use the same game for: Professional, College, CFL and AFL type games. Hell, throw in some mutant league sports for all I care. At the core all these games are the same. But just generic them up (allowing of course the community to "customize" to their hearts content). Of course, we then brought up the recent fantasy baseball stats ruling regarding whether or not those are public domain. It seems that lawsuit would only help in this regard (I am not a lawyer)
Just as an exercise in business and programming, the hype in the gaming world would be unmatched by someone sending a big FU to both EA, the NFL AND the NCAA all at once.