A rewrite would probably benefit the performance and abilities of Wordpress but it would be at the cost of ALL the themes and plugins. The platform would start again from scratch. I don't follow Wordpress too closely but I haven't heard of any one talking about - or having the energy for - such a rewrite.
Would Automattic even allow such a rewrite to go through? It would be a horrible transition for Wordpress.com.
As for alternatives... There are a number of good CMS with a well designed, easy to use admin panel. They aren't popular though, plugins are scarce and support is uncertain. This often makes Wordpress the best choice by default. Which is kinda sad.