On another (non Amiga) Commodore forum a member has just announced he purchased a bundle of Amiga 2000 stuff from a former Supra software developer.
One of the most interesting things was that the Amiga 2000 he purchased seems to have a triple OS installation. Upon startup he can choose to boot into Workbench 1.3, 2.1 or a DEVELOPER'S RELEASE of Workbench 3.0.
As far as I know, Workbench 3.0 for the older ECS Amigas has never been archived (or known to exist?). It seems he has both a copy of the kickstart and the beta OS in his machine.
I have refrained from posting a link or details until I get his permission to forward these.