Special Events in Summoner's Rift

On the title, by special events, I mean something that suddenly happens during gameplay. Something like meteor showers, invading monsters, hidden treasure, or perhaps a boss fight more threatening than Baron Nashor that would take both teams to eliminate. I've seen games do this before so I was wondering if Riot could give these events a shot.

Doesn't really have to affect the gameplay. It could just have visual effects like when you visit Urf's grave in the earlier Summoner's Rift designs except something bigger.