There are folks within Sun/Oracle doing exactly that. One effort, Project Jigsaw, is aimed at splitting the large rt.jar into smaller modules to reduce the number of classes loaded on startup. Here is an update from last December:

http://blogs.sun.com/alanb/entry/is_the_jdk_losing_its

Somewhere in there is a comment that says the JVM loads around 300 classes to run an empty main class.

I'm curious to see what the merged HotSpot+JRockit JVM will look like in a few years.