So, do you think this editor is finished? I would be sad if this was really the fate of the program! :(
jessicochan is busy with other stuff, so updates will come when he can get to them, for bug fixes only. he does not plan to add new features, the engine is now just in maintenance status.
as to the open source, he has said before that he does not plan to release the source code.
so if you mean "the editor is finished" as in "dead" then no, i dont think so. if you mean "the editor is finished" as in "feature complete" then yes, it's finished.
it is capable as is of making good games. it's not perfect, and doesn't have all the features that some of us would like to see, but it has achieved its goal of enabling people to make simple wolf3d / doom-ish retro fps games. there are bugs, alot of bugs, and they will be squashed eventually. give him time.