I'm afraid I also find this comment confusing. Is it an artist cache? It looks like it's recreated every time ```draw``` is called so I'm not sure why it's kept as an instance attribute. I appreciate this is not new functionality, however your changes mean the values in the dictionary are no longer matplotlib artists. Correct me if I'm wrong, but a ```LineCollection``` is an Artist, but the gridliner_elements dictionary now also contains a dictionaries of lists (albeit containing artists).

I agree you want to make the ```Text``` instances available, but it may be simpler to ```update``` the gridliner_elements dict with the key/value pairs from ```labelset``` rather than introducing another layer.