So you think hacking QT libraries like this (and not from the outside, I mean internally) and using C++ would make a good community editor? http://doc.qt.io/qt-5/qtwidgets-richtext-syntaxhighlighter-e...

When using QT for a highly modular editor be prepared to code QT components from the lowest level. It's not like you take a QT widget and modify it on a simple way. Trust me.

If you think it is easy to code editors look e.g. at the people who write letters and their custom editor tool: Microsoft Word. Now look at the many competitors this program had and how many behave super speedy on all plattforms.

I've written low level GUI components for several UI frameworks before, thank you very much. It's not that bad and a lot smoother for the end user.

The real problem is this new generation of "developers" that only know Javascript. When all you have is a hammer...