I am usually checking on Googl^w Bing Maps and Wikipedia whenever a specific landmark catches my attention - much more fun for me personally 
While I am not against the idea for a better POI system later down the road (more interaction possibilities, filter by categories etc.) it doesn‘t have much appeal to me currently (compared to other wishes).
And I have POIs deactivated anyway during flight.
That being said, there is a community fly-in event where the organiser took the effort to create custom POIs (with the FS SDK) specific to the „Back in Time - World War II“ theme!
That was nice indeed. So yes, there are definitively use cases for an extended POI system.