In practice there is often little need, the same distros/packages the Pi can run are almost all, if not entirely, available for x86 as well. I usually just write code on my main Mac or Linux computer/VM and run the exact same code on the Pi. I guess it might be interesting as a technical exercise, but actual useful applications would be limited. Raspian (the OS most Pi users run) is a fairly vanilla Debian distro to work with, and also has an x86 version if you _really_ wanted to match the Pi that badly. The Pi of course can run mainstream distros like Ubuntu etc as well.

The only usecase I’ve ever really encountered is building armhf Docker images for Pi use, but even that can be done relatively easily now on x86 machines with qemu without emulating an entire ARM machine.

I’d argue a more useful thing for many Pi users would be a decent test library for stubbing GPIO calls, would make writing code that interacts with the GPIO on non-Pi machines much easier. This should be relatively simple to create, although I’ve yet to find a good one.

Qemu can emulate the Raspberry Pi - there's instructions here: https://azeria-labs.com/emulate-raspberry-pi-with-qemu/

You know you can get the cloud implementation for free, right?