Oh in terms of GAMEPLAY the event will be interesting, no doubt on that. I mean, just look at these new items for the gamemode...
But in terms of lore I barely expect anything to move, unless they make the event resonate until Halloween, when it's time to bring out the Shadow Isles again as Bilgewater's primary involvement with the world is their proximity to the Harrowing.
But the timeframe is too big, so they either get another event (Probably a noncentral region such as Ionia) in or they will do what they can do best and simply do nothing.
Freljord and Shurima have proven it that Riot has no idea how storytelling works in their medium. I don't even have a bachelor (media-science) yet and could write you a 40 page thesis about the possibilites you have with the tools you have when working with this kind of thing. (In my method I view it as a system with things you can do and things you cannot. I call it "clockwork analysis". How does it work and what can we make it do?)
The most puzzling thing: It could be so easy. The community does not want cinematic trailers all the time. Sometimes they just want a short story. Or a moment of a champion being silly. A text describing a encounter between champions, maybe directly or as a tale. Summed up those small drops of lore form the world and the constant stream of small releases keeps the audience hungry, yearning for more.
Also, there needs to be more lore in the actual game. Medial Para-texts are fine from time to time, but if something is not "in the game" it is somewhat "less worth" in the viewers perception (unless we go full cross-media storytelling and establish a serious frame, such as an animated series could do).
We need more voice-overs. More taunts, more item flavour texts, more seemingly useless buffs (think of "this champ is a flipping ninja"), but with biographical importance. Imagine playing a champ that is a criminal and you have the buff _ Branded for the murder of High Councellour XY_
Just because the type of game does not favour typical linar storytelling it does not mean that we cannot establish and create personal stories and represent them inside the game.
Going back to the buffs. Imagine a lore event that involves a murder and several champs are suspected. During several court-protocols the suspicion wanders from champion to champion. Until now, nothing so special. But what if. IF they all get "buffs" in the game, like "suspected of killing xy. Under survelliance by the orders of Piltover Supreme Court". Those could vary as "assumed main culprit", "Witness" or whatever...
But. Those buffs change whenever a new piece of the story is unveiled and the positions change.
Well, that's just one idea from my side here, I might be getting a bit too worked up about this. If I, a single dude that sometimes writes fanfics, can come up with enough ideas that could keep lore running, then what is narrative even getting payed for?