Possible Solution for the Lore RetCon Problem
When the DevBlog about the Lore Retcon was posted, the boards have been flooded with negative reactions to it. The Institute of War and the League of Legends is what made League of Legends unique. It's the reason Garen and Urgot could fight on the same team, or why champions from different parts of the world are in the same area at the same time. Basically, there's two opposing sides. The Narrative Team likely doesn't want to go back on its plan, and the community seems to want to keep the past lore.
So what I propose is a compromise.
The Narrative Team said that the past lore including the Institute of War, Journals of Justice, and League of Legends is hindering their storytelling because they don't want summoners to seem like all-powerful beings controlling champions.
The community wants to keep the lore because it's what makes League of Legends unique and having all the past lore suddenly un-canon just doesn't make sense, and creates a divide between story and gameplay.
So, why not just get rid of the thing causing the problem with the narrative team's storytelling? The summoners.
Keep the League of Legends, the Institute of War and the Journals of Justice, and link the new lore. Remove the idea of summoners from all of this, that way the champions aren't being controlled by all-powerful summoners, but the lore itself, and the thing that made LoL unique stays in-tact. Instead of summoners, the players would just be "role-playing" as their champion, who happens to be competing in the League of Legends.