Now that you have opened Pandora's box... allow me to ask why we don't really try to replace wxFlatNotebook with wxAUINotebook. Just for consideration.
wxFlatNotebook has served us well in the past, true. It is themable to a certain extend, true. However, it does have a few smaller issues too, and we compile and link an extra library when we already compile and link another library that has similar (or better?) functionality built-in.
I don't know how mature the wxAUI notebook/tearoff code is, but I guess there's enough review now with it being in the mainstream package.
What I would love to see, too, would be to have some control (no matter which) own editors and that's it. The application should not know whether an editor is shown in a tab or in a tear-off window. Why should it know, anyway?
Also, remember how much code was necessary (and how many problems occurred and had to be fixed) to implement split-view editors. Would it not be nice if the application just created two editors, told the AUI window manager to stack them, and then told one window to forward events to the other? No keeping track of anything, you would not even know that you have split view enabled. Or what about having 4 or 5 views of the same file open? Even that should be possible without a lot of hassle.
OK, to be honest I could not imagine having 5 views of the same file open, but I don't use split view anyway (confuses me big time). Still, would it not be cool if it just worked?