-* [a patch](https://lists.debian.org/20181202212535.GC11687@gaara.hadrons.org) has been proposed for dpkg to mark packages built on "merged `/usr`" with a `Build-Tainted-By: merged-usr-via-symlinks`;
-* the reproducible builds team has added a "merged `/usr`" variation to their setup, and have then [tagged](https://tests.reproducible-builds.org/debian/issues/unstable/paths_vary_due_to_usrmerge_issue.html) the Debian packages from unstable which had differences due to "merged `/usr`". It seems that ~61 packages were affected by differing builds; 32 from these have been fixed in unstable already.
+* [a patch][https://lists.debian.org/20181202212535.GC11687@gaara.hadrons.org] has been proposed for dpkg-buildpackage to mark packages built on "merged `/usr`" hosts with a `Build-Tainted-By: merged-usr-via-symlinks`;
+* the reproducible builds team has added a "merged `/usr`" variation to their setup, and have then [tagged][https://tests.reproducible-builds.org/debian/issues/unstable/paths_vary_due_to_usrmerge_issue.html] the Debian packages from unstable which had differences due to "merged `/usr`". It seems that ~61 packages were affected by differing builds; 32 from these have been fixed in unstable already.
+
+## The long-term desireable situation
+
+TODO: prose the ideas below, I haven't had enough time.
+
+Given that hosts with different top-level directory schemes already exist; there are various ways forward.
+* Flag-day to get all hosts on "merged `/usr`", through a base-files version; probably in buster+1 (bullseye)
+* Disallow "merged `/usr`", let users who ran `usrmerge` on their own
+* Let Debian converge to a situation where non-"merged `/usr`" Debian hosts are equivalent to symlinked "merged `/usr`" hosts; do this through upgrading all packages shipping files outside of /usr (but exceptions) to stop doing this. Could be achieved by setting policy for buster+1 (should) and buster+2 (must), or maybe even shorter. This would make the symlink "shortcut" migration redundant.
+* Support both "merged `/usr`" and non-"merged `/usr`" systems forever: this implies that our packaging tools need to either support countering effects of "merged `/usr`" (e.g. through manipulating PATH for builds to detect files only in their .deb paths) or identifying tainted packages, and letting installing users decide (warn or error out at install time).
+
+Given the repro build tests, it does not seem impossible to enforce that official Debian packages support being built on either "merged `/usr`" or non-"merged `/usr`" systems; however, due to Debian being upstream to many other distributions, and due to `.deb` packages (which often don't go through the same level of checking and policing as official Debian's) being built by ISVs, our users will probably face similar problems to what we have described.
+
+It's bizarre to have official buildds be non-"merged `/usr`" while user hosts will converge to be more and more "merged `/usr`".
+
+## For buster