It would be nice if the jenkins plugin would support the "new" notifyCommit feature in addition to the current trigger implementation.
https://wiki.jenkins-ci.org/display/JENKINS/Mercurial+Plugin (see the Push Notifications section)
Similar features exist for the git and svn plugins.
Ideally if this was implemented it could be either a global configuration or per repository configuration. (We would prefer a global configuration since all our repositories are built on one build server, but I could see others having a need for a per-repository configuration).
Definitely not a big deal; it would just be one of those "nice to have" features.