Take the blender player exe, a seperate exe that plays games. obviously its possible to split out some of blenders functionality into a seperate binary.
Probably need an understanding of linking and an idea of the structure of blenders code, these sort of things are more hack work, adding if-defs etc.
If your realy keen, go ahrad, probably do some research then put it to the BF-Commiters as how you intend to go about it. - you dont have to have general support, but youll realy want this to be in BF-Blender, so might be good, also get some advice from other developers.
It would be nice to have a blender renderer that would work with only basic libs. then you could keep support for currently unsupported Os's, BeOS, SkyOs, hobby OS's could easerly port the renderer and add it to there list of supported apps, not like this is the aim, but it wouldent hurt
Render binary would be small, I have got a full blender distro to 3 meg bzip2, so Im guessing the renderer would be less then a meg compressed.
Mabe sombody could impliment the render deamon and get it to launch the render only binary, as a seperate project of course but would make the small render binary more attractive, mabe we could have a render node distro, under a meg and supports many OS's.