I've read some forum post saying that at SenchaCon it was announced that after GXT 3, Sencha would focus on making GXT work for mobile apps too? Is this true or just a rumor?

At first, GXT for mobile would look like a self-competing product for Sencha (for its Sencha Touch and Sencha Architect) but if we look closely, if possibly, GXT is a product for developers wanting to develop web (and hopefully mobile apps) using Java, which the latter Touch and Architect is for Javascript developers.

I have developed some apps with plain GWT and with GWT mobile framework, and with PhoneGap its really possible to build interesting mobile app, the only problem I have with the existing GWT mobile frameworks is the lack of continuous development and lack of maturity in such mobile framework. So I am guessing that if GXT would support mobile, it would take the proven framework with it and Java/GWT developers can start building great mobile apps.