I spent a bit of time to develop a new unofficial gatling mqtt plugin. Based on the one from mnogu listed in your extensions.
It is compliant with gatling 2.2.3, it provides new features for performance testing of mqtt based services. I will try to maintain it and follow new versions of gatling:
I would be pleased if you can add it to the list of extensions. And also if someone from the community is interested to review it, that would be great.
Thank you !