So far on xemacs-beta the current plan is to make Finsert (and
presumably any other buffer insertion function that accepts
chars) signal wrong-type-argument when presented with an integer.
As for the ?\ooo read syntax, \ooo should be allowed for \000-\377.
It should fail with some kind of read syntax error for anything
over 0377. This keep compatbility with 8-bit XEmacs, and doens't
break the abstraction layer for whatever the wide char turns out
to be.