On Wednesday, October 28 at 10AM (PT) Batman: Arkham Knight will be re-released on the PC. A posting on the Batman Steam Community page gives you the details on what to expect when the re-release rolls around.
AR Challenges
Crime Fighter Challenge Pack #1 Crime Fighter Challenge Pack #2 Crime Fighter Challenge Pack #3 Batmobile Race Tracks Arkham Episodes Story Packs Skins & Batmobiles