Those features could be baked into existing tools and test runners (unittest, py.test, trial, …), but that might involve a lot of redundant work.
Python already has a de facto standard generic code coverage tool, coverage.py. One of the great things about it that it can invoke any Python tool or script and collect configurable coverage information about its execution, without any special support from the tool being invoked.
Could this same generic approach work for reverse coverage?