Introducing a new format specifier for every typedef will quickly exhaust the alphabet.
Of course, there would be performance implications - not to mention the added complexity for implementors.
[1]http://www.gnu.org/software/libc/manual/html_node/Customizin...
You could work out all sorts of namespacing and automatic reassignment schemes, of course.
I can't think of anything without trade-offs off the top of my head (I double that anything exists), but in my (limited) experience it's very workable.