Most mobile devices currently have not web socket support for web apps (I believe PhoneGap gives you a wrapper to a native socket), so there isn't much value in Sencha Touch receiving web socket support at the moment. Ext JS 4.0 will have a WebSocketProxy as part of the new data package.
It sounds like you could just use normal, low-level web sockets for a chat app - there's not much on top of them that Ext JS would give you in this case.
FYI - iPhone's iOS 4.2 Safari is supporting Websockets... a high mark for smart phone competitors, and also the reason for support at the framework development level too ! IMHO !!