Those familiar with Myerson's thinking say that he is trying to beef up Microsoft's mobile presence considering the growing importance of mobile in the business world. While Microsoft currently dominates on the desktop, it has a long way to go to do the same in mobile.
It's not known if Microsoft plans on merging the UI of the two operating systems or if it will keep the user experience different depending on the size of the screen in use.
Tweet from alleged Microsoft insider claims a merger between Windows RT and Windows Phone is coming
source: @MSFTnerd (private) via WMPoweruser