Nickolay Platonov of Symbie has developed an extremely interesting bridge between Joose and Ext. The cool thing is that he has overriden Ext.extend to bootstrap all Ext classes to be full blown Joose classes. Meaning you can easily inherit from them using Joose facilities and especially apply roles to ext classes and object.
More info can be found in this post to the Ext forum and check out the joosified Ext samples.
Nickolay's approach can, of course, be applied to any JS framework that provides a pseudo-class layer so I'm looking forward to joosified YUI, Prototype, etc.
Merry Christmas! Long live the Joosification.