What if someone maintained an online "virtual museum" of old emulated machines and operating systems? This could be done as SaaS, with some value add tools for converting to modern formats thrown in.
Amusing, interesting for history's sake, and possibly useful, but licensing issues would kill it for closed source, and it's not needed for things with permissive licenses because you can already get the source for old versions and run it yourself.
Some people would pay for something already set up for them. Microsoft might like the idea and support it, as it furthers their backwards compatibility story.