I wish there were real high-quality Linux and Windows themes imitating Windows 3.x, 98 and XP (and some other old OSes perhaps) realistically, not just "kind of like that". I would even pay money for such if I were satisfied.

Ideally, they should also be easy to combine in different ways. E.g. I want Win3.11 pixel art icons, Win98 window&panel styles and WinXP non-antialiased fonts - these 3 things make me feel orgasmic.