One of x264's developers is
busily working on implementing the YUV444 colour space into x264, and relatively recently a third party has
put together a patch to get it to work with RGB colour spaces as well.
The most recent releases of ffmpeg
support decoding YUV444 h.264, so programs that employ it (VLC, ffdshow, etc.) will probably, in the near future, be built to support it as well, which would allow us to consider deploying encodes in that colour space on a wider scale. I don't believe this is presently the case for RGB colour spaces, and I'm not aware of any efforts to get those implemented into ffmpeg, so looking at RGB would be a while off.
In the meantime, I'm encouraging encoders to experiment with using YUV444 and see if they get better results (in terms of visual quality vs. disk space used) when making use of it.
---
EDIT:
YUV444 and
RGB support has landed in x264's trunk. Presumably builds of this will be available soon, for all you Windows types. :)
