More suggestions of things to do

XML::Validator::Schema gets my vote too, expecially WRT namespace support.
PPI needs a lot of work in the lexer.
You could port File::Remove ( abandoned since 1998 ) up to File::Spec, so it might actually work on non-Unix platforms.

That's just a few to get you started. The first too might be a little advanced, but File::Remove could be a good place to look. Write a shitload more tests for it, then start to move it to File::Spec usage.