I worked on UTF-16 and UTF-32 encoders, but now I'm off my developing computer. I'll provide updated patch soon.

I think that only "surrogateescape" and "surrogatepass" error handlers have need in optimization, because they are used to interpolate with other programs, including old Python versions. "strict" stops processing, an optimization is not needed here. All other error handlers lose information and can't be used per se for transcoding bytes as string or string as bytes. They are used together with other slow code (for example for encoding string in XML or HTML you first need to escape '&', '<' and quotes). It is easy to add fast handling for 'ignore' and 'replace', but these error handlers are used largely for produce human-readable output, and adding it can slow down common case (no errors). That is why I limit my patch for "surrogateescape" and "surrogatepass" only.