If Ao Shin really does get released in 2016

Well, let's look at this logically... Singed is likely there with the chemical warfare that was used. Riven obviously was. Swain is one of the most respected generals, and he wouldn't need to be physically present to make an impact. Possible Warwick was involved, but that is more tenuous. Urgot fought so often and sustained such garish wounds that he had to be made into the thing he is now somewhere, and it is just as likely that was against Ionia as Demacia without anything to say otherwise.

Then you get into the Du Couteau family and their likely involvement in Noxian conflicts and business (which means Talon and Katarina could make an appearance). Not to mention Mundo and Zac could both have been present.

Not to mention that any way between Noxus and somewhere else is likely to further instigate violence from Demacia against Noxus because it would make sense for them to time a greater investment against Noxus when they are already involved in a war on another front. Or the fact that, ideologically, Demacia and Ionia have several different points of mutual agreement and make one of the most probable alliances against the Noxus/Zaun alliance. (If number of champions is any indicator of relative military strength, Zaun + Noxus would be stronger than any two other city states, which would necessity alliances between factions that are at war against Noxus/Zaun to increase the odds of realistic victory.)

I'm not saying that an Ionia event would have to include a lot of Noxus or Demacia, I'm say that it would make the most sense for it to include all of that. A large scale conflict between a Demacia/Ionia alliance and a Noxus/Zaun alliance would arguably be one of the best lore events that could happen (much like a large event to counter the Harrowing from the rest of the world against the Shadow Isles and the armies of undead from there would make a GREAT event).

Further, Noxus is constantly changing based on the outcomes of the conflicts they are involved with because of how Noxus is run as a city state. The strong rise to the top, the weak are discarded. So anyone involved with the invasion of Ionia who failed would be in a very awkward place upon returning defeated which naturally creates a point of conflict in Noxus itself from the champions who return as failures.

I'm not saying that it would make 0 sense to have an event just for only Ionia or Zaun or Demacia or Noxus. I'm not saying those events couldn't be good or even great events. I am saying the BEST event would include the conflict between all of those groups because that is what makes the most sense because there is no way to fully illustrate the effects of those conflicts by showing only one of those groups. Bilgewater and Shurima may be large self-contained independent entities that aren't that involved in world politics... The same cannot be said for Ionia/Noxus/Zaun/Demacia. Largely because of the conflicts that exist between all of those nations.