I see. So you mean, we should be able to see who's premade on their team?
Reply what benefits you think this would have on the game and the players. It's all about game health. Would you like enemies to know if you're duo with your friend? I think it makes an extra this to worry about. Riot probably does not want people to change their play style based on who is partnered. Like, if you have a top laner and a jungler duo it's likely that the jungler will gank top a alot more. Knowing they're duo the top laner would be more passive right? Riot wouldn't allow hints like that to be made.
Or do you mean, balance duos with duos and trios with trios. Which is already implemented. Fivequeue almost always get matched with another Fivequeue or Fourqueue with one player with a slightly higher MMR.