-* [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`", trough 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.
+
+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