Let’s start a new thread to discuss the revival and extentions to humanoid_msgs. It seems like Vigor’s StepTarget.msg has parameters that more closely match what most groups are commonly using.
An RVIz plugin sounds like a great idea! Most packages are using Visualization Markers for footsteps, but that has been pretty limited in my opinion.
As for humanoid kinematics/dynamics, it seems like Simox VirtualRobot is a lightweight and actively maintained library that has these calculations. There is an example ZMP preview controller based on it https://github.com/TheMarex/libbipedal.