Mount Targon who are the other two champions?
I only see four options either two new champions (most likely one a new champion and a champion we already have with rework for him). Beginning lore for 5 people (http://leagueoflegends.wikia.com/wiki/The_Great_Barrier) MOST LIKELY
and
since they have ties to mount targon/great barrier , some sort of Event , or maybe hopefully a NEW MAP (not just skin/theme for one). I guess a 5th option is any combination of these. Really hope its a new map but i don't see it happening but maybe since they did take Dominion down for this new map?
during the harrowing or
&
during burning tides last year,in that their lores won't be updated with this event.