So finally we have a game system file for Warhammer Fantasy! Available to download over at data.battlescribe.net.
Disclaimer: I don't actually own a copy of Warhammer or even play it, so I have inferred the details from around the internet and from a friend's Skaven army book. Please let me know over at the UserVoice page if there are any problems, or even better, fix up the file and send it over to me at feedback@battlescribe.net.