That's a fascinating question, actually, and probably beyond my ken. I can say that none of the code is in there but the WinFS team includes many veterans of that effort. The WinFS design today reflects many bits of hard won knowledge that team earned.
One very important similarity is the inclusion of standardized schemas.
So you are talking about WinFS' Schemas. I am currently working on "How to view business objects (in a particular application context) through the WinFS API ?".
I've read in the documentation that the Extensibility wasn't supported by the build 4051. Is it right ? Or is it just still undocumented (I mean undocumented in the Visual Studio Documentation) ?