Cool. This looks very similar to what I have described here:
http://tinyurl.com/3l8eh
Some comments/ideas:
1/ Personally if I were to develop such a system I would make it relatively
independent of the underlying build tool (Maven, Ant or anything else). It
would sit on top of any of those tools.
Update:
Found maven:reactor source code at: org.apache.maven.jelly.tags.maven.ReactorTag
I still don't know how Jelly figures out this is a jelly tag but this
is obviously the appropriate code.
ViewCVS link to relevant directory is:
http://svn.apache.org/viewcvs.cgi/maven/maven-1/jelly-tags/trunk