I really like the ping system on League of Legends, it can be utilized for all sorts of things. However, I feel that it is a system that can have tons of changes to improve gameplay.
My first suggestion is to have the pings show up on the actual game. By this, I mean on the actual screen, and not the minimap. On the screen, I'd see it as something like 4 green arrows coming down onto a green circle, just a quick little animation that wouldn't interfere with gameplay, but would be able to help players specify designations for their pings. (I.E. "Go to this bush" *ping*) The pings on the minimap are quite large, and it is easy to mistake what a player means when there are multiple bushes in the area. I feel like this would not be hard to implement, and would be extremely helpful for coordination plays. I made a sad little drawing in Paint to try and help visualize my idea.
My second suggestion is a bit more complicated, and I'm not sure how it would be achieved. If you think back on any Real Time Strategy game you've played (I.E. Age of Empires, Robin Hood, Starcraft, etc) you have the functionality to make your unit 'patrol'. With this command, you set a number of waypoints on the map, and then the unit will follow the waypoints. While I'm not suggesting the same thing, as it would make no sense, I suggest a way of implementing the visualizations of this. In other terms, if you begin a game and, for example, click on the minimap to go to the dragon, you will see your icon following a white line for its destination. All I am suggesting is a way for players to use a ping from one waypoint to the other. I'm sorry if I am confusing, I don't exactly know how to explain it. This implementation of waypoints could be used to strategize with the team, and improve coordination. (I.E. "Taric, go from here to here to here" *Use the waypoint button or whatever, click three points, press the waypoint button again, and the path will visualize on the minimap*) This would probably be harder to implement, and I don't even know if possible. I just think it would be nice to have.
Anyways, once again, I love the ping system and feel that there is tons of ways for it to be modified and improved. Thanks for reading!