In the end I did upgrade this and fixed a issue that JLR changed the API, so reverse GeoCode calls no longer work, but you can still get the longitude and latitude back if you want to use the location. The rumoured blocking of third parties did not happen and it was fairly trivial to upgrade.
It is tested and has been working but use at your own risk and support may be challenging when the old car goes, so I won't publish to the plugin store unless somebody needs it.
https://github.com/neilkplugins/JLRInControl-indigo-plugin/releases/tag/2022.0.2-AlphaNeil