I came back to this post while searching sth about extjs, and have to say a little about it. I started using it since v1 till now as the writer, and i agree with every single word. However though, things are getting a bit different as of now in mid-2019. Modern toolkit got parity with classic toolkit, theming is easier, performance is pretty good, open tooling, extreact and extangular are good gains as well. I also see the release of ExtWebComponents a big step forward.
Licensing is still an issue, but there is at least a community license now and you dont have to pay for 5 devs if you prefer subscription. I still expect more towards regaining community back though.
I am not that sceptical about the acquisition anymore, after 2 years passed. I believe, extjs will go on the path it deserved, maybe late but not too late. I hope that Idera won’t make a big mistake again as sencha did before.