Location field is something I'm working on for a customer. They have a LOT of location fields in their plans, and because of the recent Google announcement that GMaps won't be free for high-volumes, I'm looking into a Cesium JS integration for this.
To use it, it would require that you run a Cesium JS installation (a lot of overhead).
I see...that's still a tough one to deliver. Right now, the Joomla API has provisions to implement field plugins within components. No provision exists within the API to implement them within plugins or modules.
My extension allows a developer to implement custom fields within the subform, but not field plugins (because again, the API makes no provision for such things).
Depending on the field, I might consider writing articles describing how to implement those fields within a subform XML definition. Basically, the subform can contain any native Joomla field type, and can contain any field type defined within the XML. So there really isn't any limitation other than having the ability to code a field within the XML, which is easy enough to describe.