What's the benefit of that? I see downsides: have to deal with the FSF, have to work with the existing codebase, have to fight to get the changes accepted, etc. It can always be ported into gzip if that becomes desirable.
have to fight to get the changes accepted
One of the main reasons I stay the hell away from OSS unless I can fork it.
The FSF is not involved in the development of zlib. Moreover, pigz and zlib are maintained/developed by the same person.
Non-sequitur? gzip != zlib
gzip ~= zlib, It's the same authors and the same algorithms.
That was exactly my thought when seeing the website.