I'd like to keep it as it is. But I'd like to see a converted version too in order to do benchmarks. :)
It's mostly just for designer friendliness I'd consider changing it.
I don't think there's anything complex enough about it that it warrants a .theme.
But I suppose that's kind of hard to say, since most of the complex themes out there are being implemented in phptemplate, and the template.php file makes it more flexible, and still copy-able (which the chameleon theme doesn't).
IMHO it is worth to keep a "showcase" (even if such a simple one) in core of such an important feature as the native PHP themes. It shows the versatility of the theme system quite well. If only phptemplate based themes are going to end up in core, it will be a hard time getting out the perception from some guys' minds that Drupal is phptemplate oriented. Goba