I'm really interested riot?

Riot's released a great many cinematics, and a lot of them are outsourced. A lot of time spent making cinematics comes in to the rendering, and while I can't say how much time Riot's renders would need, it's probably a long time. More than a few days, at least.

We'll probably get a cinematic in 2016. But don't hold your breath.

The only reason ''A New Dawn'' cinematic was made is because of the Summoner's Rift map update, they wanted to do a commercial to show the people that the game is not the same outdated crap that it was before and the map is new. There is no reason or any benefit for them to create a new cinematic for nothing, unless if they ever bring a new map or anything then maybe but currently there is no point especially now that Tencent bought 100% of the game they are focused only on marketing.