"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Windows Phone 8.1 Adds Support for Apple's Passbook Passes
As noticed by Tom Warren of The Verge and reported by iMore, Microsoft has created a method that takes the data from a Passbook file and converts it into a card that is imported into Microsoft Wallet.
Windows Phone 8.1 supports Apple's Passbook natively. I've been using it for flights. Works perfectly pic.twitter.com/MFScqvEVU7— Tom Warren (@tomwarren) April 14, 2014