Jesús, did you have any particular idea about exactly where these new
features would be useful? Or was your idea that someone needs to read
through the code and check whether the features can be used at all?

Also, it should be noted that the scope of this issue has grown somewhat
since it was created - zlib 1.2.6 was released recently, with more new
features. And it seems that the zlib folks sometimes add new features in
point releases (e.g. 1.2.5.1) as well...