I believe that the perfect story to establish the LoL universe in cinematic form would be the rise and fall of the Shurima Empire. I know it's too early to talk about movies but we can only imagine! The title would be something like "Shurima: Ascension." And would tell the story of young Azir until his demise on the great golden disc.
Just imagine Xerath burning Azir's father with his guards and saying: "Look on my works, ye Mighty, and despair!" (I'm just kidding)
I think there are alot of stories in this universe which would qualify for a movie, not just Shurima. And probably that scenario wouldn't even be the best choice.
I see 2 options.
Option 1: Make a series of movies, each dedicated to a region and its "main plot".
That would include your idea of Shurima and the awakening of Azir, trying to bring Shurima to its old glory. Zaun and Piltover could have a plot mostly focusing on Piltovers finest and Jinx or Viktor trying to find Ekko to convince him to collaborate. Demacia and Noxus being in a big war with each other. You get the idea.
Option 2: Make one movie and try to pick a plot which is influencing as many regions as possible.
In that concept, Azir and Shurima wouldn't really be the main focus in my opinion. Shurima doesn't really have an impact on other regions, their champions mostly interact with each other and don't really have strong ties with champions from other regions.
Main plot could be the Void trying to invade Runeterra. Mount Targon would probably have a huge part in this movie, since they are the main antagonist of the Void. They could include the story of Nami trying to find the Aspect of the Moon (namely Diana). But since the Void is a global threat, many regions could be included in that movie. Shurima being a part of it. It could be interesting to see small Void invasions in each region and we are seeing how the champions are dealing with them before creating an alliance to stop it together.
The story could be centered around a big war started by Noxus, since they basically try to conquer the world. Demacia would have a big role in that scenario, too.
I also think Shurima would be the best choice for a movie plot.
Shurima is one of the most progressing regions of LoL and It has many tragedy that could work for a movie. And animation wise, It would be satisfying even for a not a lore fan person (or at least not a Shurima fan).
Can you imagine the fight between Nasus and Renekton versus Xerath? Oh boy. It would probably be last minutes of the movie.
Making film would be extremely expensive: -Hiring a good director -Paying for beautiful scenes -Taking care of actors and actresses Without them, the film would be bs So, making a film will be very hard for Riot, or the film makers that copyright from Riot
