ROS Melodic promises to be a big release. Because of that, we’re starting the process for the release a bit early this time.
A proposal for the minimum requirements and targeted architectures (aka REP3) is available here. This release will potentially have some larger changes in it (move to OpenCV 3.4, the use of C++11 and newer in public APIs, etc). We welcome feedback on that draft proposal from developers, maintainers, and any other interested parties.
Your friendly ROS release team