I'm not sure if such thing is already planned, but I could not find any trace of it on the docs and web pages.

In some use cases it is necessary to create variants for an application on the fly using the API rather than just defining them by hand. One more thing that makes a lot of sense is a way to manage categories for an installation (=device).

All of these are already (kind of) possible to be done using API, however I could find no Java client like the one that exists for Sender API.