A lot of existing (leaked) x86 mobo schematics are already available to anyone who cares to look. I don't think there's much "secret sauce" in a standard PC anyway, at least at the component interconnect level; it's almost like one of the worst-kept-secrets in the industry. There is a lot of commonality between all the designs. They might differ in the exact parts they use (e.g. VRM MOSFETs) but there's only so many ways to make something that works.