I got the NodeMCU and I really like it. After searching an IDE I stumbled upon ESPlorer and it basically worked, but the UI looks very bad (I think because it's a Java application) and I heard some devs on github are rewriting a flasher in Qt, so I created an IDE with Qt. The source code is fully free and hosted on github:
https://github.com/cybercatalyst/nodemcustudio
And this is what I scratched together after two hours of work:
I have already written larger Qt applications, for example the official graphical user itnerface for GNU Octave in 2012, so I am absolutely confident this is doable. If you have any insights from a user's point of view, I'd be glad to receive your input.