With the rapid development of HA, things seem to break often enough that I need to rebuild my software system or revert to an earlier version to keep running several times a year. I don’t know how many more times I can remove the SSD from my NUC with its fragile connectors to image HAOS directly to it from another computer via a USB to SATA cable. Ubuntu and Windows can be installed from an external drive so it would seem that HAOS could be, too. In fact, it is on the Nabu Casa Blue and Amber boxes so why not on standard x86 machines.
Another way you can image it is by booting into a live distro from external USB storage, and either downloading the HAOS image that you want to deploy, or having it available on the same external boot device.
For example, you can create a live Ubuntu install with persistence on a USB flash drive, pop the HAOS image on there, and keep that handy for when you need to re-flash. From within Ubuntu, you can use the gnome disk utility or something like Etcher to write your image.
If the OS is not totally broken, you can downgrade it via the CLI.
Thanks, I now see that the instructions have been updated at Generic x86-64 - Home Assistant , method 2 to do exactly as you recommend: boot the NUC from a USB stick containing a “live” installation of Ubuntu Linux and from there download the HA OS installation package and flash it to the NUC’s installed SSD with Balena Etcher.
I’ve used this method to flash an x86 thin client that has non-removable eMMC. It’s a handy thing to have in your tools arsenal. Also, if you want to be able to easily add/change your bootable tools, check out Ventoy. It allows you to boot many ISOs and adding them to the boot menu is not necessary - you just copy the ISO to the drive that Ventoy is installed on.
Hope this works out for you 
I do think that there should be an x86 installer for HAOS that can boot from USB/ISO.
I would maybe look at DietPi as an example - it appears that they just use CloneZilla to create a super simple ‘installer’ that deploys an image of DietPi. I imagine that it would be fairly straight forward to do the same for HAOS. There are probably simpler ways of doing it, but this is the first thing that came to mind.
I reckon this would be good for both newcomers and experienced users. For the latter, it could be a nice time-saving tool.
Any thoughts on this?
I think Home Assistant should offer a single package that would be downloaded to a USB drive for a one-step intallation of HAOS on a bare metal x86-64 machine or to write over any existing OS on such a machine. Since Windows and Ubuntu do that, I know that the tools exist but I don’t know enough to recommend a particular one.
My view is that we in the open source, open standards, local control, own-your-own-data home automation community are in an existential battle with the Big Tech companies who want just the opposite. We’re beating them in the variety of devices we can connect to and in the extent of communication, control, and computation tasks we can perform, but we’re lagging in some areas of ease of use. Mind you, the HA operating UI is both easy to use and easy to configure, and HA keeps improving its ease of configuration and programing. In fact, I switched to HA from openHAB 3 years ago for exactly these reasons. But some installation and configuration tasks are still challenging. Selling controllers with HA pre-installed is a great advancement and a big help but, with the rapid improvement and proliferation of computers, there will always be users like us who will want to use a different computer. So it should not merely be possible for a skilled hobbiest to use other computers for Home Assistant, it should be easy for a person with only basic computer skills, just like it is to install Windows or Linux on them.
FYI, DietPi installation is exactly like you describe - boot from install media, agree to a prompt, it clears the target disk, then it deploys its image. Interestingly, they appear to have HA in their CLI quick package installer, though I’ve never tried it.
The nuke-and-replace install method definitely has its place, and it does seem like HAOS is an appropriate example. I think as long as the raw images are still provided for those who prefer a manual approach, a simplified ‘installer’ would be a pretty awesome addition.
I did look at OpenHAB too a while back, and went with HA. I want to look at OpenHAB again at some point, but HA seemed like the less time consuming choice. Ironically, I got sucked into it hard, so not much time saved 
but of course, in a good way.