Shouldn't that have already been do-able? I know the The MOnSter 6502 is a thing. The 386 I have no idea about though, that's to far out of my wheel house.<p><a href="https://monster6502.com/" rel="nofollow">https://monster6502.com/</a>
A replica 386 would be impractically large - it's got around 275k transistors, compared to the 3.5k in the 6502. At the same scale as the MOnSter 6502, that'd be about a hundred square feet of PCB.<p>The number of layers isn't even remotely close to being a constraint. The real i386DX was manufactured on a process which only supported two metal layers, and a PCB version isn't subject to the same constraints as silicon.