CEGUI is nice but I think it is better to improve our own GUI system that integrates perfectly with all existing code. CEGUI should be a plugin you can use if you want to.
I thought about what to do next, after 0.5 is finished. The first thing some people wanted me to tackle is Android support. Here we have the conflict: The rendering engine needs to be rewritten first or else it would mean porting the engine twice.
That means the following road map might be useful:
1) Rip out the old rendering pipeline and replace it by the new one
2) Get the 2D system to work with the new renderer
3) Rewrite the editor to use the new rendering engine (Which toolkit? Qt? Our own GUI system?)
4) Port the player to Android and Emscripten