Arch, just tries really hard to not break stuff. But there are some major changes that usually break upgrades for a brief window of time (usually announced on the main page if known, otherwise fallout on forum/irc/etc). Derivatives (manjaro for example) tries to hold back packages for a certain amount of time before moving to the main repos.Speaking of Arch: how does Arch avoid the problem we have with occasional build fallout and some packages becoming temporarily unavailable due to dependency breakage.
I understand how Debian does it, but Arch seems to do what FreeBSD does, but with less (no?) fallout.
Alpine, has a concept similar to FreeBSD/debian, with stable branches and a rolling branch (which is similar to the stable branch of freebsd).
So all in all, the FreeBSD option looks good, but in can be improved. PKG really could benefit from a review of the solver (and resilience of the sqlite backend).
As is, and barring the issues with packages occasionally ghosting for a while (or dependencies not correctly defined) I think the latest tracking of base, ports and kmods is working fine.