I love the idea, and I love strong visions, but why not something closer to Motif/CDE? In my mind at least, when I think of 90s workstations, I don't think of Windows 95.
More current-day developers are nostalgic for Windows 95/NT than for Motif because of sheer exposure. It's the same for me: Windows NT UIs have a vibe of "good old days" for me, whereas Motif UIs feel like ancient history that is unrelated to me personally.
I've never used a pre-OSX Mac but still find the screenshots lovely. I've even styled my Linux window decorations after MacOS 9.2. I find it an optimal middle between heavily retro and modernly sleek themes.
Not a MacOS type UI, but I like WindowsMaker, which tried to emulate NeXTSTEP.
The whole UI was a lot more complex, and IMHO, probably the best-looking GUI ever designed. There's an effort to bring it back to life via GNUStep, and as a desktop environment, NEXTSpace: