I don't see the point in changing the various conversion APIs in the unicode database to return Py_UCS4 when there are no conversions that map code points between BMP and non-BMP.

In order to solve the problem in question (unicode_repr() failing), we should change the various property checking APIs to accept Py_UCS4 input data. This needlessly increases the type database size without real benefit.

For that to work properly we'll have to either make sure that extensions get recompiled if they use these changed APIs, or we provide an additional set of UCS2 APIs that extend the Py_UNICODE input value to a Py_UCS4 value before calling the underlying Py_UCS4 API.