KissMyAssets, I pre-ordered it from the same windows store page you linked.. Hopefully it works out cause it is on my windows account and with the "play anywhere" I think it should work. Don't quote me on that though.
i also pre-ordered it there and i should be able to play it on the 23/9/16
it also says this.
Supports Xbox Play Anywhere: yours to play on both Xbox One and Windows 10 PC at no additional cost.
ULTIMATE EDITION OWNERS WILL HAVE EARLY ACCESS TO THE GAME ON 23/9/16. PURCHASE THIS OFFER BEFORE 27/9/16 AND RECEIVE 2 CAR PACKS AT NO ADDITIONAL CHARGE: Forza Horizon 2 Rockstar Car Pack (Xbox One) and Forza Motorsport 6 Meguiar's Car Pack (Xbox One).