Is there a way to serve in-house ads based on the current user's location?

Hi hyphalos! :blob_wave:

Regardless of the context of an existing or hypothetical ad plugin, there is a built-in feature for this in Disourse available from the admin view of a user profile:

The endpoint is: https://your-discourse.com/admin/users/ip-info.json?ip={user_ip}, with a GET request.