Having decided to move away from ExtJS, I've begun re-writing ShiftEdit from the ground up using jQuery UI for the widget components.
Behold a screenshot of the rough prototype:
As you can see we have a familiar interface including panels, tabs, menu and a file tree.
I've made use of several excellent projects including:
There is a lot to do and I will update the blog with my progress.
If you feel you can contribute the source code repository is available on Github. Only the front-end is currently available, so you will not be able to connect to a server and edit files just yet.