Drupy: "Drupal" in Python

In other words: wouldn't it be better to try and improve it, instead of making the same mistakes Joomla, Wordpress and Drupal all made and try for some real extensibility?

I'm sure it's not for everything but for me it's worked really well. It handles all the CMS bits in a nice way and you can still write custom Django bits when you need to.

Seems to be pretty popular with clients so far (out of a sample size of 2 for me)

I loved Drupal when I was limited to building sites in PHP. It worked around a great deal of common problems in PHP, and was well documented with a good community, etc...

Still, most of the advantages came from having a semi-regulated environment to use to implement CMS projects in PHP. Once you have a sane language like Python, it would be a huge waste to do a direct port. The result would be profoundly unpythonic, and give you no particular benefits because of it.

If you adapt it to make it more pythonic, then you lose the benefit of familiarity for new users. As it is, it's not really like you'll ever be able to use existing Drupal modules in a Python reimplementation; even if you could, it's hard enough keeping modules working across different versions of Drupal, much less entirely different platforms.