Your friendly neighborhood navigator here. I wanted to mention a new great set of features as a collaboration with the community in Nav2! Jacksonk9 @Stevedan and afifswaidan have worked with me build out a new costmap and collision checking API for Nav2.
New to the Nav2 Simple Commander Python API is a Costmap2D object which can take in published messages from a subscription and process them into something easier to utilize for your pythonic needs. It also contains a collision checking object that can take in the output of a footprint publisher (or custom polygon) and check for collisions in the given costmap - just like the C++ version does in the costmap_2d package.