We all know Ao shin was supposed to be the first real dragon champion in the game as stated by riot but he was scrapped for a few reasons:
1) Ao Shin's kit just didn't pass muster. This is a pretty common problem we run into in the initial stage of champion creation, and while sometimes we can adjust on the fly (a usable 'paper kit' might have two or three core abilities that make things click), other times we need to shelve the entire concept and take a step back. Internally, we call this 'ice boxing' a champion until we can revisit with a fresh perspective.
2) delivering on the unique shape of a serpentine dragon's body - long and powerful - in a game where instantaneous turning is key presents some unique technical challenges. Given enough time, we were confident we could solve the turning problem, but because Ao Shin's abilities weren't coming together we were reluctant to commit to engineering work that might just end up scrapped.
3) The biggest reason- we committed too early to Ao Shin's premise without really developing his thematic roots. Around the time we announced Ao Shin, we were in the process of slowing down our champion pipeline to figure out how to continue delivering resonant characters that feel unique to the League universe. We learned a lot during this time (still learning!) and when we examined Ao Shin with these new lessons - Why was he in Runeterra? What were his motivations? - we unearthed a fresh thematic that really set us off running.
At the time they released the info on Ao Shin these reasons make sense considering the year (late 2013) and the technology available but its been some time since and Riot has come a long way so I personally think this champion could be brought back.
The first point just seems lazy given how its pretty much saying "we tried and didn't care enough to keep trying" there's a lot of people who can come up with ideas and you can even get inspiration from the community.
Now I get the 2nd point the most but with riots current technology wouldn't it be possible to make this serpentine dragon? (Vel'Koz and Aurelion sol come to mind) The [concept art](https://imgur.com/sHew3q5) looked good already so putting him in game with a few changes (or even none) and animating him would be very possible right?
The third reason is also I think as a 2013 issue considering saying his thematic roots didnt fit into the lore but an Ionian guardian who descends from the sky in times of great crisis would fit quite well as quoted from the league of legends page about Ionia "the border between the material and spirit realms tends to be more permeable here" meaning a guardian dragon doesn't seem too far-fetched.
In conclusion I feel like bringing back the storm dragon would be a really cool idea and the reasons why he was scrapped don't seem relevant in the current year. Aurelion Sol was kind of a disappointment as he doesn't feel very interactive and for a celestial dragon of unfathomable power who birthed light into the universe, he seems pretty lackluster in terms of his kit. A divine storm dragon sounds very imposing and lightning effects are very flashy (ha) and really badass in my opinion. I want a dragon who when I see on the rift, I think "damn, thats impressive" instead of "look at this clown playing aurelion, lemme just walk up to him and he dies"