I think having identical handling for two different socket types split between two different packages is fine, especially if one of those packages (s6) is a dependency of another (s6-networking). I don't think it's crazy unless you're duplicating the socket handling code itself and since s6 is a dependency I'd imagine you could pull that into a library, either in s6 or skalibs. I guess I'm seconding your suggestion to move libs6net and the unix socket stuff into s6, then pull that in to s6-networking as necessary.
As for the overall layout of the s6 family of packages, I think the granularity is ok as it stands, especially with this proposed change. One gotcha you'll run into though is that now s6 will probably fail to compile against musl without the the sabotage headers, at least if libs6net requires netlink. Cheers!
