Does Sencha Touch support Windows 8?
Yes, Sencha Touch 2 supports Windows Phone 8.1, Microsoft Surface Pro and RT. Actually, Sencha Touch 2.2 and up even supports Internet Explorer 10 and Windows 8.
That also means support for tablets running on Windows 8, IE10 and up.
Mind you we have very nice out of the box themes for Windows Phone!
(It's probably similar for Ext JS 6 Modern toolkit and up.)