It would be an interesting experiment to run, because MDI died around the time that 1024x768 was a big screen. A lot has changed since then.
Although, arguably, one can get most or all of the benefits with a multi-workspace window manager and a workspace running a tool & document program by itself.
Thinking back, I remember using the MDI mIRC and having an active channel in its own window. The rest of the channels and lists were inside the mIRC application. I then had my chat up with whatever document I was working on.
The thing from that kind of setup that is hard to come to today is a simple way to designate some windows a less important than others. The important ones get into the task manager/dock. The unimportant ones are grouped with other similar windows.
I can't think of a major desktop that I've used that lets you do that. It seems to be all or nothing. I've seen docky and some KDE plasmoids get kind of close.
"Sets" are interesting here because it is a return, the long way around to MDI in a way, but with years of learning/experience of task management from modern taskbars, IE/Edge tabs, and other thoughts on task switching. I like the idea that in Microsoft's opinions Sets are more useful as diverse collections of heterogeneous applications (a Word document and its OneNote notebook and its Edge browser research tabs together in one window) rather than the classic MDI homogeneous approach. I think that may be the welcome modern twist the MDI concept was missing originally.