According to Mastercard’s website:
MasterPass by MasterCard is a digital wallet service that makes online shopping safe, easy, and convenient. MasterPass stores all your payment and shipping information in one central, secure location. With MasterPass, you can shop, click, and checkout faster online.
No date has been put forward for when MasterPass support will arrive, but if and when it does, it will certainly make Microsoft’s Wallet app a lot more useful for those wanting to use their Windows Phone/Mobile device for tap to pay transactions in stores.
We will keep our eyes open for any developments on this!