I created an experiment:
I copied all module_utils (except C#/PowerShell; and six, since the collection loader will barf if that’s around somewhere outside ansible.builtin…), doc fragments, and the action plugins/modules related to package modules that do respawning (i.e. apt, apt_repository, dnf, yum) from stable-2.16 to a collection and adjusted the imports, and some more smaller changes (mostly related to how arguments are passed to Python Ansible modules, and new hidden _ansible_* parameters added in ansible-core 2.17).
That way, I hope that respawn also works with Python 2.7 and 3.6, since there should be no syntax errors coming from module utils.
Can someone try GitHub - felixfontein/ansible-py2736compattest (the collection is called felixfontein.py2736compattest) to see whether it works as I hope?