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.
When it comes to the renderer, how about the BGfx render lib -> https://github.com/bkaradzic/bgfx
Here some notes from the author what the render lib supports link-> http://www.godotengine.org/forum/viewtopic.php?f=9&t=43&start=10#p352