It's important that the "displayed" form of an address be identical to
the way you spell it when you type it in. ...
On my Swedish keyboard there is a key for the
letter A WITH DIAERESIS.
10646 is so broken that "A WITH DIAERESIS" could be encoded with
two characters of "A" and a combining "DIAERESIS"
or
one character of "A with DIAERESIS"
Situation is much more complex with non Latin characters.
So, 10646 is practically unusable without tremendous effort of profiling,
which, I don't think, worth doing.
Masataka Ohta