I’ve written those plugins for some of our in-house devices. Key points:
You have to tell Ansible where your plugins are, either using environmental variables or via ansible.cfg
You’ll need a module that actually uses your plugins
The ios.py (in plugins/cliconf and plugins/terminal) is a very good start, the corresponding module is modules/network/ios/ios_command.py
getting the regular expression in the terminal plugin (in variable terminal_stdout_re) right is critical - start with something really generic and work from there, if that regular expression doesn’t catch the prompt you’ll get weird errors about timeouts (even though the ssh session connected fine).