> We'd need to expose the UCS4 APIs *in addition*
> to those APIs and have the UCS2 APIs redirect to the UCS4 ones.

Why have two names for the same function? it's Python 3, after all.
Or is this "no recompile" feature so important (as long as changes are
clearly shown to the user)? It does not work on Windows, FWIW.

> I haven't checked, but it's certainly possible to have a code point
> use a non-BMP lower/upper/title case mapping, so this should be
> made possible as well, if we're going to make changes to the type
> database.

OK, here is a new patch.  Even if this does not happen with unicodedata
up to 5.1, the table has only 175 entries so memory usage is not
dramatically increased.
Py_UNICODE is no more used at all in unicodectype.c.