hint at a more funky install

howto/new-machine-cymru.md

@@ -214,6 +214,12 @@ See [howto/new-machine](howto/new-machine) for post-install configuration steps,
 
 IMPORTANT: Do not forget the extra configuration steps, below.
 
+Note that it might be possible to run this installer over an existing,
+on-disk install. But in my last attempts, it failed during
+`setup-storage` while attempting to wipe the filesystems. Maybe a
+`pivot_root` and unmounting everything would fix this, but at that
+point it becomes a bit too complicated.
+
 ### boot setup
 
 TODO: in the last attempt at following this config ([ticket