I wouldn't expect so. All you get of third party parts on the schematic is the names of the pins, and that generally isn't kept secret. Sometimes the detailed functional descriptions of each pin are, but generally not anything you'd see from the schematic.

If you look at the Open Compute project, there's full schematics available for boards that have far more interesting parts than what would be on this.

Intel has become notoriously secretive with their documentation over the years, so I think that is very much the issue here. The 8086/8 were very open, but they started closing off little bits at a time after that. "Appendix H" in the P5 era was the first major sign of it. Bits and pieces have leaked out over time, but they still want to keep a lot of it secret.

For comparison, someone has made an entire 386 PC motherboard himself: https://news.ycombinator.com/item?id=29273829

I suspect there's enough information out there publicly to do everything up to perhaps a PIII (Socket 370 era) or thereabouts, but it starts being much harder beyond that.