5. In order to solve this problem of protocol tyranny and hijacked implementations, Wu suggested that for the future of bitcoin to remain beautiful and grow, the community will need multiple implementations.
Satoshi was against multiple implementations.
https://bitcointalk.org/index.php?topic=195.msg1611#msg1611.
I don't believe that we should religiously follow everything that satoshi says, but I've seen a lot of people like jonald_fyookball talk about satoshi's support of larger blocks, so I thought I'd throw it right back.
If the second version screwed up, the user experience would reflect badly on both, although it would at least reinforce to users the importance of staying with the official version.