There aren't any technical limitations to adding multithreaded decompression zstd. We just need a compelling enough use case to justify the work it would take t

There aren't any technical limitations to adding multithreaded decompression zstd. We just need a compelling enough use case to justify the work it would take to add it. pzstd is now obsoleted by zstd -T0, but it offers multithreaded decompression for files compressed by pzstd (it will still be single threaded for files compressed by zstd).