That1MiningGuy found evidence for an upcoming points-based King-of-the-Hill mode on the map’s moving train. As with each data mined leak, nothing has been confirmed by Respawn Entertainment, and things tend to change.
Data mined information is technically true at the time of being found, but most information are just placeholders. Respawn Entertainment tends to change things up as they go as we've seen with multiple leaks for future Legends and their kits.
It seems Mirage will be the star of the event, but it's not known whether the train will be changed like some of the town-takeover events. Changing the train is a bit different than an actual town, but it's still pretty effective.
Apex Legends unveiled these type of events back in Season 2 and it was a massive success. It only makes sense they would bring it back for Season 3.
Photo courtesy of Respawn Entertainment