Something I'd observe here: without expressing an opinion about PEGs vs regexes, I'd note that regexes are much more widely used. They're also completely sufficient for an awful lot of text processing tasks. PCRE regexes would be a great inclusion to the stdlib, and would probably be popular.
> PCRE regexes would be a great inclusion to the stdlib
Why? Anything that can be done with a regex can also be done with a PEG, and the PEG will be much more readable.