Quote: "next-gen fps does this"
Yeah, but nearly every next-gen fps has an online mode, where they use the same quality model in the online multiplayer where others can see the gun. Are you implying that in online mode the player can see the high poly model with the faces cut off, and others see the same model except as a complete low poly version? I don't know exactly, but lets not forget that modern day fps games now have thoasands and thoasands of polies.
http://www.rsart.co.uk/2007/08/27/yes-but-how-many-polygons/ Sid Sinister suggested this site to me anout a poly count question I had, and (though some of these games aren't FPS) they are still modern day games with a different camera placement, so they might be able to do this. Yet, I still don't think they use that much of a high poly model, I mean they probably do what you did Demon Air, a high poly, then low poly, and so on... Here's an article on how they made (mainly animated) MGS4:
http://features.cgsociety.org/story_custom.php?story_id=4735 If you read the article there is a lot of interesting things, but the point is that modern day games are just that high poly (Heck, Resident Evil 4, on the Gamecube, had Leon at about 10,000 polygons). And just as another reference, an image taken from Wikipedia about Leon in RE4
But I'm just saying is all... I could be wrong on what I'm saying, but based on the info, I'm assuming I'm right, so please correct me if I'm wrong...
