I hope this is true, but the devs never explained the details. They only mentioned it as an ‘unranked game mode’. The devs needs to clarify what elo is used. Until then we can only guess.
Since even the lobby uses unranked elo, i dont really think the elo for this game mode is really hidden. I think it is much more likely that quick play uses unranked elo (but i already found some counter examples, i will add a quote to another post of mine at the end of this post) or it uses no elo at all.
i am not surprised at all if we will see a lot of threads like this in the next weeks. I am not convinced about this new feature.