Pretty nice and rewarding once you can first join your own server :-) Can confirm that the protocol is a mess. Also expect it to change massively between major versions, including new data types or shuffled packet ids. I've created a parser for Python and is was too much work to continue supporting beyond 1.8. Code is at https://github.com/dividuum/fastmc

I would guess one part where parallelism might help is interleaving of packet parsing and (de)compression if they exceed the compression threshold.