Source? Where/when was this confirmed?
EDIT...found it here
https://batman-news.com/2014/03/05/batman-arkham-knight-include-batmobile-skins/
Doesn't look like much yet. Different color and slightly different shape from the completed Batmobile. If they do other Batmobiles (Nolan, Burton, Animated etc...) I hope they give them as much detail as they did to their own Batmobile. I'd hate to get an 89 Batmobile or Tumbler that feels tacked on and low-res compared to the game's main version.
Just dreaming here, but it would be great if they released a SDK for the PC version (or even for consoles somehow!) so fans can add their own Batmobile models. I've got a few that are almost ready to go (would need some updating to be as detailed as current gen allows though).
EDIT 2: We already know they've got basic 3D models of quite a few Batmobiles on file:
https://www.sideshowcollectors.com/forums/showthread.php?136694
The makers of this arcade game borrowed RS's AA Batmobile model for their game, so I see no reason they can't return the favor for AK. But like I said before, as cool as these models look, they'd need to be updated. They're a little too "soft" and light on the detail level for the current gen.