"If someone was getting ready to fork a second version, I would have to air a lot of disclaimers about the risks of using a minority version. This is a design where the majority version wins if there's any disagreement, and that can be pretty ugly for the minority version[...]."
https://bitcointalk.org/index.php?topic=195.msg1611#msg1611
" I don't believe a second, compatible implementation of Bitcoin will ever be a good idea. So much of the design depends on all nodes getting exactly identical results in lockstep that a second implementation would be a menace to the network. "
https://bitcointalk.org/index.php?topic=195.msg1611#msg1611