You ask "Is Maven the ultimate Java build tool? Is there more it should do?".
I reply "Something is finished, not when there is nothing more to add, but when there is nothing more to take away". I think Maven 1.0 should do less - a lot, lot less.
I think the concept of a project description is a sound one, but the implementation in Maven troubles me deeply. It seems as though the developers have tried to shoehorn everything they can into version 1.0, including a scripting language (Jelly). In my experience, this is very, very bad practice - you have an large system where everything is too new and there's no mature foundation being built upon.
Ant is an incredible, industrial-strength build tool. I think a good approach would be to create a very thin layer over Ant itself, perhaps using XSLT to translate the project.xml into build.xml and using a simple batch file to bind it all together. Bundle it with Ant and you have the best of both worlds built on the solid foundation of Ant itself with very little overhead.