I might be in the minority on HN, but I think that WordPress is doing fine just as it is. Whereas my gag reflex kicks in at the mention of a Drupal contract, WordPress is still pleasant-ish to work with. It's simple enough that I can get my own custom work done without having to spend a ton of time fighting the core system. Though, YMMV depending on the nature of the custom application, I'm sure.
I think it's the perfect example of "worse is better" approach. Yes, it might not be perfect, but it does well what it says it does, it's quite simple to customize and you just upload it online and you are set. Being nice internally is good. Being working with tons of available plugins is better.
The 'upload and online', however, is and will continue to be the killer feature that will keep rails/python/java/etc-based CMS at a major disadvantage.
Starting projects today, I prefer Grails. Starting a project which I had an intention of distributing to a wide number of users (potentially for eventual world domination), I'd use PHP. Nothing else comes close to the ease of getting the widest number of people able to upload/install.