Yes, there are many things to do on all ends. Starting with refactoring the main engine, cleaning up the editor code, writing documentation and improving the build system.
The biggest pain will probably be getting the engine more multithreading friendly. There are already primitives for multithreading and thread communications but I don’t think they are ready and complete enough to provide a completely multithreaded engine.
The renderer needs some work and optimizations, maybe we should even create a completely new one from scratch to deliver deferred shading.
Another big pile of work is Android support as well as Emscripten support.