Lumping these together because the meta protocol may influence how to best implement pipelining. I have left out random bug reports/issues related to MaxIdleConnections since they're all resolved by this work.

I left a bunch of generic pipelining notes in: bradfitz/gomemcache#160

For reference, clients that implement the meta protocol (and also sometimes pipelining)
https://github.com/QuangTung97/go-memcache (new client)
https://github.com/yeqown/memcached (new client)
https://github.com/bobrovde/gomemcache (fork)
bradfitz/gomemcache#151 (pull request on this repo, their own work has substantially diverged though)

Meta protocol examples:
https://docs.memcached.org/protocols/meta/
Meta protocol definition:
https://github.com/memcached/memcached/blob/master/doc/protocol.txt#L79