Has anyone announced a way to run Mojave on Apple Silicon yet? Or will that just never happen?
In what way?
There’s no possible way it will ever boot natively, because it’s 100% Intel code.
It might, theoretically, be possible to have an Apple Silicon Mac boot an ARM build of macOS (e.g. Ventura), and then run an emulator (like QEMU) in there, which could in turn boot an Intel build of macOS.
But I don’t think anyone has gotten this to work at this time.
I found a Mac-based emulation platform (UTM), which can create VMs (via QEMU), emulated systems (also via QEMU) or host VMs via Apple’s virtualization library. But from what I’ve been able to determine from its documentation, it can only run macOS 12 and later as a guest, and only as a VM, not an emulator. So that won’t help here.
I also found a blog post and its followup article from someone who got PowerPC Mac OS and Intel Windows running on Apple Silicon.
But after a bit of web searching, it appears that there is still no easy way to get Intel macOS running in an emulator. At least not right now.
Can you run Mojave off a USB stick (or external SSD) plugged into either an Intel or Apple Silicon Mac?
Intel, yes, if the Mac is old enough to support Mojave (i.e. was released ≤ Mojave).
And that’s the problem. There is to date no emulator/VM to run Mojave on an AS Mac.
Even newer Intel Macs might be able to run it through a VM.
But you’re right that a native-boot will require a Mac that meets its system requirements.
The technology behind Intel chip emulation has to get a whole lot better before it will result in a usable emulated system. I don’t see that happening any time soon. One-time translation technology used by Rosetta works great for applications, but doesn’t really play well for an operating system (an operating system is a very dynamic beast internally).
UTM/QEMU can emulate Intel chips, but they aren’t modern ones, and the emulated operating system has performance you wouldn’t write home about. Except maybe to complain about it.