Float texture support is partially implemented in trunk on svn – pass in
[NSDictionary dictionaryWithObject:SyphonImageFormatRGBA32 forKey:SyphonServerOptionImageFormat]
as the options to SyphonServer (see SyphonServer.h).
What isn’t finished is the fallback to something that works if a client or server is in a GL context which doesn’t support float textures – otherwise it should work, and I’d be interested to hear how you get on with it.
We’ve discussed CPU-side pixel access a lot. The main concern is that direct access may open up an opportunity for a client app to block a remote server app indefinitely. We’d prefer people do buffered read-back in OpenGL – draw into FBO, download to PBO(s) – which is what we do in Syphon Recorder.