I concur that this would be useful to have.

I was sure an environment variable $CHANGE_LOG did exist but nope. It would be super useful.

If you are interested in uploading your build to HockeyApp (with release notes and some other stuff)
You may try my plugin at: https://github.com/ohoeltke/hockeyapp-plugin
Will try to update the binary this weekend, master branch is current

For info, there's a workaround in this StackOverflow answer:
http://stackoverflow.com/a/11837662/234938

While I don't think this would be universally useful, it should be fairly easy to write a plugin that does this.

I'll try to put something together in the next few weeks.

@Daniel
I suppose this is a case for the SCM-API plugin instead of the core.

So… it has taken much longer than originally expected, but in the context of today' Hacksgiving community event I wrote a simple demo plugin that should do what is requested here. It has not yet been published to the Jenkins community update site, but I pushed it to GitHub:

https://github.com/daniel-beck/changelog-environment-plugin (mvn verify should build it)

FWIW there's also a quite flexible list-changes command for the Jenkins CLI (https://wiki.jenkins-ci.org/display/JENKINS/Jenkins+CLI)

No response for over a month, so with the public release of the plugin source code I consider this issue resolved.