In my opinion, the lack of a clear roadmap (correct me if I'm wrong), and estimation of upcoming releases is -by far- the biggest downside of working with ExtJS.
It would be awesome if there was more information available on whats going to happen and when(-ish). And I mean a more continues stream of information.
Not:
Januari: It's gonna be march we think
Begin April: Oops... But its gonna be very soon we hope
May: Release
But:
January: It's gonna be march we think
February: Well, we were to optimistic, at least a month delayed
March: Told ya so..
April: Yea we're sure, its gonna be within the month
May: Release
However, I think this is a repeat request and is to much to ask