Just posted these on the Qcubed forums but I think there might be some people interested here as well.
There seem to have been previous attempts to get the ExtJS grid and TreePanel working with Qcodo and in a Qcodo way the results can be found here:
http://www.qcodo.com/wiki/file:old_downloads/qform_controls/qextgrid_for_use_with_the_ext_js_library
http://www.qcodo.com/wiki/file:old_downloads/qform_controls/qexttreepanel_for_use_with_the_ext_js_library
Since they are from 3 years ago they might not work out of the box with the latest version of Qcodo, but they seem very interesting and quite complete judging from the demo's.