> but for writing a complete application I would want to develop in my language/editor/ecosystem of choice
For well over a year now, you can use an external editor (VSCodium or whatever) and set it in Godot settings (so that clicking a script icon in the scene tree opens that file, and clicking a signal handler in the properties pane jumps to that line), and the LSP for GDScript (which is hosted by your running Godot instance, and which your editor's LSP client connects to) has been excellent back when I last dabbled in it.
For well over a year now, you can use an external editor (VSCodium or whatever) and set it in Godot settings (so that clicking a script icon in the scene tree opens that file, and clicking a signal handler in the properties pane jumps to that line), and the LSP for GDScript (which is hosted by your running Godot instance, and which your editor's LSP client connects to) has been excellent back when I last dabbled in it.