i believe adding something like this to this add-on will make it even better:
Now Audentio Has done this to keep there clients themes up to date, an add one API based links to your account via API key and checks what products you have from them.
with the add one you can install & update the themes on your site without actually uploading it your self.
now i would suggest 2 different options:
Option 1: just enter in your account details Or ApI into one of the all ready pre-configured Known API sites that support this kind of thing
Option 2: Configure the API your self, so if you have paid Addons from a site you know of, you can get there API details from them and configure it your self either it is Account based login or Key + there API server URL
and any other config
and as an addition to those features i suggest support for third party Sites URL's instead of the domain Xenforo when adding the Resource URL inside the Update form of the add one
this would be a great combination with the ability to Store Third party Credentials besides xenforo Credentials alone.
this way you will be able to use the update feature from third party sites...