Consider distr1 for an image-based rather than package-based system

https://github.com/distr1/ puts together a whole Linux system using (currently: uncompressed squashfs) images.

I am wondering whether we could use it to

* Put together a Live ISO that would contain essentially a folder of images
* To "remaster" the Live ISO, we would just have to add/remove/exchange some of the images
* At installation time, just copy over that folder of squashfs images, and have a modifyable/updateable system (by putting each FreeBSD pkg into an image)
* Being able to put together `.app` bundles by just putting the relevant images into the bundle

This would

* Speed up Live ISO generation significantly
* Simplify Live ISO generation
* Speed up CI significantly
* Speed up package management on the installed system
* Still allow us to use something vaguely similar to AppImages/`.app` bundles for applications

Can it be ported to FreeBSD? (I've been interested in FreeBSD lately because it is much more of a consistent platform than the various incompatible Linux distributions.)

Additional food for thought:

* Can the distr1 approach benefit from ZFS? (For example: If we make `.app` bundles that contain a bunch of images, could ZFS deduplicate those with less overhead compared to having deduplicate all of the files without images?)

cc @stapelberg (hi @stapelberg. I am the AppImage guy. With hello, I want to make something 10x as good.)