Atm moment i see the next variants:
- Review private tokens and define whether they can be removed at all, i.e. BUILD_NUMBER seems duplicates existed job variables
- migrate generic tokens like BUILD_LOG_EXCERPT to token-macro-plugin
- keep as is some tokens that depends on global Email-Ext hudsonUrl configuration it impossible to make them generic
- keep as is JELLY_SCRIPT and SCRIPT. Both depends on templates in JENKINS_HOME and SCRIPT is a bad name and may conflict with some cases. So create new GROOVY_SCRIPT token somewhere (even separate plugin because it will depends on config-file-provider?).
That should keep backward compatibility, GROOVY_SCRIPT may obsolete SCRIPT (using files in JENKINS_HOME imho is bad design future) and provide other plugins ability to use this tokens without having dependency on email-ext-plugin