Daniel,
I'm missing a more detailed comparison to the mentioned rsync/librsync/zsync libs/progs. The most important differences between rsync and librsync/zsync is that the former can do interleaved patching (search for matches / data transfer). It seems go-sync doesn't support this (yet) or it's just not mentioned in https://github.com/Redundancy/go-sync#commandline--files?
Andrey