I’ll explain why this should be a thing. Back in the day, on Warcraft 3 DOTA; the most popular mode was -ar (all random). -ap (all pick) mode was mostly for noobs or players wanting to learn/experiment certain builds. Just based off this statistic alone should be reason enough to include this, and it wouldn’t require much extra resources to accomplish.
The all random mode could have restrictions, like minimum 1 healer/support and 1 tank/bruiser, or leave it to complete random and enjoy the madness. Either I would enjoy.
Now the next argument would be, why make this mode ranked? Well statistically it is known that people do enjoy their leaderboards, it simply makes people want to play more even if its 1 more game or take the game more seriously, this is true for any game really.
I do play the brawl even when I’ve done the weekly just because I enjoy the randomness, but the matchmaking can be quite one sided; having a ranked mode would ease this pain for more experienced players.