Plan for "distribution set" deprecation

Hi everyone,

With pkgbase landing in 15.0, I decided that it's time to announce the
timeline for deprecation of the legacy "distribution sets".  Here's the
plan:

15.0-RELEASE:
* PKGBASE becomes the default in release/Makefile and a new NOPKGBASE
option is added.
* The installer supports both install options, with dist sets marked
as "legacy" in the pick-how-to-install menu.
* The disc1 images only contain a pkgbase repo; people who want to install
from disc1 without pkgbase will need an internet connection.
* The dvd images contain both dist sets and a pkgbase repo suitable for
offline installation with either mechanism.
* Traditional FreeBSD Update will work for the entire 15.x branch, including
security updates, since this is relatively easy to do as long as we have dist
sets.
* Work is underway to make freebsd-update behave as a wrapper around pkgbase
on pkgbase-enabled systems (right now it just refuses to do anything).

16-CURRENT around 2026Q4:
* NODISTSETS becomes the default in release/Makefile and a new DISTSETS
option is added to enable them.
* support for dist sets in the installer is disabled by default (build
option to re-enable).

16.0-RELEASE and later:
* Legacy distribution sets are not included on any release media.
* Install images only support pkgbase.
* Legacy FreeBSD Update does not exist on 16.x; users will need to
pkgbasify their 15.x systems before upgrading to 16.x.
* Code for distribution sets remains in the tree so that it can be used
by downstream projects which aren't on pkgbase yet.

17-CURRENT around 2028Q4:
* All the dist set code gets removed from main.

Note that this is all about releases and binary updates; the traditional
process for updating from source (installworld and friends) is not expected
to change in the near future.  It's possible that *eventually* that will
move to a "stage the world, package it, and then install the packages"
approach (just like ports moved from installing directly to "staging" over
a decade ago) but if that change happens there will be ample notice.

-- 
Colin Percival
FreeBSD Release Engineering Lead & EC2 platform maintainer
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid