So for those of you who, like me, didn't know what Bencode is, here's the description from wikipedia[0]:

Bencode (pronounced like B encode) is the encoding used by the peer-to-peer file sharing system BitTorrent for storing and transmitting loosely structured data.

It supports four different types of values: byte strings, integers, lists, and dictionaries (associative arrays).

...

While less efficient than a pure binary encoding, bencoding is simple and (because numbers are encoded as text in decimal notation) is unaffected by endianness, which is important for a cross-platform application like BitTorrent. It is also fairly flexible, as long as applications ignore unexpected dictionary keys, so that new ones can be added without creating incompatibilities.

[0] https://en.wikipedia.org/wiki/Bencode

Bencoding is as human-readable as MessagePack, but not as concise. I don't see why would anybody choose bencoding today.

Oh, and it doesn't guarantee that your message will fit in a single line. JSON can be encoded to a line.