All the parts have now been committed. Thfr@ will probably finalize his patch for "nicer" github/gitlab/whatever during our next hackathon.
As far as things go: bsd.port.mk(5) explains what's going on. If DISTFILES.sufx is set, then MASTER_SITES.sufx will be used. Compared to the "fixed" list of MASTER_SITES0...9, this is indefinite and possibly self-documenting (I've switched go and cargo on my machines, without any issue). The .VARIABLES construct opens a few similar issues. There's no actual hurry, but I hope to deprecate MASTER_SITES0/9 eventually: the new construct is cleaner and the relevant code is way simpler (have a look at the definition of _FULL_FETCH_LIST in bsd.port.mk)
