Looks like they've been released:
tinkerdifferent.com
Macintosh PowerBook Duo Prototype Schematics
Schematics of a 16MHz EVT motherboard codenamed Metropolis, a prototype from early PowerBook Duo development. Since it features a 68030 processor it's likely that these are very close to production Duo 210/230/250/270 models -- but be careful...
