I remember seeing GNUstep on Linux distributions 20 years ago, along with early KDE and other options. I appreciated the aesthetics of it at the time, but - can someone explain its benefits today, and why one would prefer using it?
Actually, I'm not even clear what I would replace with GNUstep, exactly.
GNUStep is not a desktop. Try NextSpace (see above) if you want a GNUStep based desktop. NextSpace is a clone of NextStep desktop.
Like its ancestor, NextSpace is fast, light and very consistent. I like the vertical menus that I can move were I need them, the dock in the file manager, the file manager itself, … It is an advanced desktop that hide the difficulties: you don't need to learn, it is logical. It is like macOS, without targeting beginners.
I am a long time KDE user, I know how it works, it is my desktop of choice. But there is still some glitches, and it is a different user experience than NextSpace.
Actually, I'm not even clear what I would replace with GNUstep, exactly.