While there is no hard consensus on what to do with CPU mining inside bitcoin, in general, I think most people will agree that 4way can go.
This implementation (with performance enhancements) lives on in cpuminer. bitcoin's 4way was only available on *nix, while cpuminer's 4way works on Windows and Linux.
I conclude that, if you are really serious about CPU mining, you are more likely to use ufasoft's CPU miner, or mine, and so we don't need multiple implementations inside bitcoin.