We need another Black Market Brawlers
No, not because it's just a fun game mode, but because it's a great way to test out new items and abilities in a casual environment. In case anyone has forgotten Dead Man's Plate
first premiered on that game mode. Originally it had to do with Gangplanks story.
Sure we have the PBE, but what if there was a permanent game mode to test new stuff? A non ranked game mode like Brawlers where we could test out new items and give feedback.
Riot has always said that the sheer numbers on live are enormous compared to the small number that get to test new stuff. This way we get some of that big number of people (the regular player base) testing the new stuff and finding out what we like and don't like before it hits the live servers.
There are so many things Riot could try out this way, and if it doesn't work it can just be scrapped later, without having to put it on the PBE or bring it onto the live servers in a later patch. How about a better Rabadons? A new AP item? An AD version of Zhonyas? An AP hexdrinker? Four new keystones? This way they can test all of them on the game mode and just see how they work and if people even like them without committing to keeping them in the game if something doesn't work out and the player base gets to really see whether half the things we want are even good for the game. Only a handful of people ever get access to the PBE servers.