Aside from the kernel itself, the Filesystem Hierarchy Standard is perhaps the only major feature common to all linux systems. Some obscure distributions modify it only slightly: stali, for example, uses a simplified version, while nixos adds too it (leaving /etc and /bin out of sight and out of direct control). Both, however, have a "/etc." You can swap out your init system, change your PATH, replace glibc with musl, pick a different window manager, desktop environment, display server, compositor, etc... But if you sit down at a running working linux machine, "/etc" will be there. You can be sure of that.
Which begs the question. What if you wanted to put it somewhere else...
In how many places, at how many levels, is the assumption of "/etc" made.
Does the kernel assume it's existence?
GLibc certainly has "/etc/hosts" hard-coded in the source. How many of these paths are there in glibc? Is there a list somewhere? How hard would if be to change them?
How much of the software on a bare bones embedded linux image is looking in there? How would we find out? Could we change it without recompiling? And then, how much more is there in, for example, Ubuntu, that would have to be changed?
Incidentally, I recall one of the first things I wanted to do when I first installed Ubuntu 10 years ago was to move /etc to /conf, I quickly discovered it didn't work like that. But if the Linux ecosystem were set up to make such a thing feasible, what might that look like?
This is a general curiosity, I'm asking in order to better understand the details of the linux ecosystem. Of course I'm not expecting a complete answer, but I figure someone might have some useful information or could point me in the right direction.