Last time I used ExtJS I was using ExtJS 3.4 and Sencha Touch 2.
The developer community was great and they patched bugs, so you updated their code.
The ExtJS community died off a little post ExtJS 3.4.
I've looked at Sencha every now and then to decide when to rewrite SaaS (zenoxlaw.com) user interface (ExtJS 3.4).
As an approach I think I'll just buy the commercial version and sign up to the latest and greatest and re develop the whole lot until it works then just stay on x release until the next major version.
On another note, I work at a large Enterprise, for internal apps can you use GPL as an approach.
Or do you just run into bugs which are not fixed until the next major release; which introduces more bugs.
So then you really just need a commercial licence to always stay up to date, to fix the latest and greatest bugs?