Thanks for asking, though the advocacy and outreach SIG is not the best place for questions related to Jenkins use or Jenkins development. The Jenkins user mailing list or the Jenkins community site are generally better choices.
Installing the incremental build will allow you to run the plugin immediately. It won't merge the pull request. Pull requests are reviewed and merged by maintainers. When a maintainer is no longer active, others can volunteer to become maintainers by adopting the plugin. The
adopt a plugin instructions provide detailed steps that someone from your organization can follow to become a maintainer of the rundeck plugin. Someone from your organization can propose to adopt the plugin and become a maintainer.
Thanks,
Mark Waite