For the record, I like XS and write in it fairly frequently. I'm mainly interested in reducing the number of esoteric things you have to learn to write extensions and I like the idea of not needing a compiler at all to write a new one. If some really good standard FFI was available on most perls, the CPAN install would be basically just copying the .pm to the right place and you're done. This would simplify the install of Gtk2 by quite a bit. It's notoriously difficult to compile on win32 because of the very short command line length restriction.

I think the Ruby FFI optionally parses header files automatically, so it may get around some of the problems you're talking about here. On the other hand, it may make them worse, since you'd need to have the development versions of package libraries installed just to run things. Gross.