You can generate a CIImage directly from an SyphonImage (a texture) output from a SyphonServer via
+ (CIImage *)imageWithTexture:(unsigned int)name size:(CGSize)size flipped:(BOOL)flag colorSpace:(CGColorSpaceRef)cs
Just make sure the GL context you init your Core Image Context with (via is shared or the same as the Syphons, via
+ (CIContext *)contextWithCGLContext:(CGLContextObj)ctx pixelFormat:(CGLPixelFormatObj)pf colorSpace:(CGColorSpaceRef)cs options:(NSDictionary *)dict
As for AVFoundation, it is a replacement for Quicktime, and sits “above” the layer Syphon works (IOSurface / Core Video). IOSurface is already integrated heavily with other imaging technologies in 10.6, and 10.7 adds a few small changes/additional features. As far as AVFoundation incorporating anything from Syphon, I have no idea why that would ever happen.
Syphon is built on top of IOSurface, and leverages some of Apples inter-process communication APIs to handle announcing frame availability. As long as IOSurface is around, Syphon will be around.