Brion,
1) You can't tell whether the update has been
applied or not
I'm not sure it matters that much, as it affects special-pages only.
Of course, having the toggle "use old schema" could be way to go. Non-
wikimedia sites should run updaters whenever they update code anyway.
2) You can't tell on-purpose blank entries from
software-is-broken
entries
You can, by seeing non-blank entries for same page, together with a
blank entry :) It is a matter of self-join, if you need to find such.
On the other hand, software-is-broken entries should be resolved in
any case, do we use empty/null entries or not.
3) Various operations on the link tables may break in
interesting ways
when encountering the blank entries
Thats where we fix them :)
A purpose-built table would be much more sensible.
The only problematic area is how application treats empty (or NULL)
entries. The other concerns would exist in any case.
--
Domas Mituzas --
http://dammit.lt/ -- [[user:midom]]