devtrackers.gg
Sorry to be the bearer of bad news in this thread. I know a lot of people have been asking for this feature and were extremely excited upon seeing this post, but we are not shipping Leaderboards in the next update.
I tracked down what happened with this particular asset and in short, the team that puts together this copy intended for this to mean, "grinding for a new rank in the new season," unaware that Leaderboards (the system) was something hotly discussed in the community. It was caught pretty soon after and the English and non-English language copies have been changed to be less misleading.
As for Leaderboards, this is a feature that I've kept on the radar of the team for a long time. About eight months ago, I compiled a large document of Ranked improvements and suggestions (which included things like Draft Pick). Leaderboards were also included as a community suggestion in this document.
So never say never for leaderboards, but for now, they're not shipping with the Formal Affair update. As with anything, we must prioritize what each team is working on for any given update. When or if we plan to implement Leaderboards, trust me, I will ensure it is part of the Update Notes Show. :)