That's one of the problems with the now-famous Fractal blog, I think: It was a joy to read in the sense that being a Python programmer, it only heightened my appreciation of the achievement that languages like Python and Ruby represent. It's what conscious, determined design gets you and what mistakes they managed to avoid. But it's preaching to the choir. If you've never seen anything other than PHP, you won't under…
So to encourage developers to start with something other than PHP you'll need to lower the barrier to entry to modifying existing software, and also make something as popular and widely useful as WordPress and MediaWiki.
This is going to take a while.