I'm not sure we can get a straight answer from ESRI on this question at his point because there is so much uncertainty with Microsoft in this area right now but "What is the future of ArcGIS Mobile for Windows?".
The concern is the diminishing future of Windows Mobile 6.x, which is probably the main platform ArcGIS mobile is designed for. When Microsoft recently announced they are changing the name of Windows Mobile to Windows Embedded Handheld, they have said a new version of this will be released in second half of 2011 and will utilize the latest development tools such as Visual Studio 2010 and Silverlight/XNA. They did say there is a clear migration path for 6.x apps but that sounds pretty vague to me.
That said, along with the fact you currently need Visual Studio 2008 and WinForms for ArcGIS Mobile development, I don't see it sticking around too much longer. I see ESRI efforts going more toward the iPhone, Android, Blackberry, and WP7 API's. Maybe the WP7 API will be the future for the new Windows Embedded Handheld OS? Any thoughts, predictions?