Making Demacia more questionable/Giving Noxus a good side
One of Riot's complaints with their established lore is that Noxus is heavily painted as evil
while the worst we've seen out of Demacia is skewed morality
and how highly they place duty over personal well-being 
So let's see what we can swap around to even them out a bit more. Grey and Grey is a bit popular in media, but it beats out Black with some fade and White with a few spots on it.
1: Make Demacia the one with the anti-human sentiments. Noxus is the city-state that does not care who you are, as long as you are strong. Demacia is deeply rooted in their traditions, so xenophobia would make more sense on them. Show that Alistar was granted a home solely to spite Noxus, and that many Demacians find his activism uncomforting. Have Poppy and Nunu (who brings Willump along) be given substandard treatment as diplomats. Make Demacia detest Zaun even further with the number of "abnormalities" in their streets. Vayne is considered a hero to many citizens for her hatred towards the "unpure." Galio and Shyvana are even more feared by the public.
2: Add some paranoia (Especially with Piltover). Piltover and Zaun have their own stories, but are also given this "Demacia vs Noxus" development. With Noxus and Zaun being proud partners of each other, emphasizing that Demacia is wary of trusting Piltover would further the differences between them while also establishing Demacia as not the best place to live. Maybe it's their trust of Yordles. Maybe Demacia is too proud to accept the sciences of Piltover so easily. You can also make Demacia less eager to claim the Averosan tribe as the accepted leaders of the Freljord, while Noxus agrees whoever has the largest army should be in charge (this would require cementing the Winter's Claw as a smaller, more radical operation).
3: Give Demacia some bad calls. I don't think retconning The Fleshing is the right move, since it is a perfect example of the Noxian mindset. And the invasion of Ionia is too important for several character's backstories (maybe too many from Ionia). Give Demacia a piece of the pie. They could annex independent land "for their safety" or take part in environmentally-unfriendly actions like mass deforestation in order to grow (Perhaps that could be the new Plague Jungles, considering the former was caused by the Rune Wars).
4: More Demacian champion lines that bring out this morality. The perfect existing example is Garen's "What we do is RIGHT" line. Maybe bring in some lines for Lux that show past her positive personality or have Xin Zhao occasionally wonder if he will ever be more than a weapon.
tl;dr With the lore revamp, don't cut out a lot of stuff and then have nothing to replace it. That's the lazy writing Riot wanted to avoid with the retcon. Also less Demacia=good Noxus=bad stuff

