Seems like a good opportunity to point out that the pun is that the RPC model is based on capabilities. Capabilities and Protobuf -> Cap. 'n' Proto. -> Cap'n Proto
Gee, all this time I thought he was hitching his wagon to the right honorable, dapper, charismatic, articulately spoken, upstanding guru of phone phreaking culture.
The pronunciation would thus be "cap [the sound the letter 'n' makes] crunch".