I'm curious, do you know which virtual machines (i.e. what emulator and what OS) you would want? Does the software exist and it's just a matter of the time to set it up? Or is it harder to get ahold of all the necessary old software (even if you have the emulator)?

Maybe in the modern age someone could make a "polarhome in a box" that offers a similar gamut of systems, but via preconfigured emulators that you can simply download and run.

On Polarhome, I used QNX, SunOS/Solaris, HP-UX, AIX and OSX. Having those running under qemu would be quite the challenge.

Until now, I have used qemu (or rather qemu-system-aarch64 in combination with binfmt-misc) on Linux to emulate e.g a Raspberry pi running on arm64. This works very well, but for e.g. Solaris or HP-UX there is the extra hurdle of getting hold of bootable media that will not freak out in the unfamiliar surroundings of a qemu virtual machine.

I have never tried, and it is possible that I overestimate the difficulty...