onie VS debian-live-config

The S41XXY-ON switches do have some complexity in the bootloader; If I recall correctly it has an "A" and "B" OS so you can update one and instantly reboot to the other if it goes wrong, as well as some ONIE functionality. So updating them is a bit of a process as you have to make sure both get updated at some point - I think they're more designed for big datacenter lights-out deployments where you have the infrastructure to manage updating dozens at a time.

I can assure you that's entirely plausible. There are many big vendors like this, with a rather smaller set of vendors that sell switch chips for them. High end network switches are effectively a commodity now, and often are not much more than a board built around a single chip/chipset, which does everything.

As for software, there are many vendors and open source projects that make complete distributions for these generic switches/chipsets.

One way to get an idea of the sheer number of devices in play here is to look at the hardware supported by ONIE, a small Linux distribution that is a de facto standard bootloader for these. Can't find a proper HCL for ONIE, but have a look at the source: https://github.com/opencomputeproject/onie/tree/master/machi...

Yes it can. Look into to config/archives/ directory (example here, though I only use official repositories for this build, it will work with custom repositories made with aptly) - and section 8.1.5 of the manual.

example config for live-build