warnings::compat is somewhat straightforward. I didn't play with 5.10 much and not sure how much of the "feature" interface can be emulated. Making this a CPAN distro will be resulted with high expectations IMHO, since pre-5.10 usage is (and will be) much more than pre-5.6. I think I've discussed a possible utf8 emulation with saper before (don't remember the details) but this was not practical too. However, adding workarounds in the code is much easier than preparing a CPAN release I believe :)