I was just about to create a thread suggesting this idea, good to see I'm not the only one who agrees we need this xD.
I think a balanced way to do this would be to select your 1st, 2nd and 3rd role preferences and also lanes you want to play (they don't always match). Then let the game take this into consideration at the moment of building teams.
But this shouldn't be an obligatory means to assemble teams, it would work better I think if you wanted to assemble your own team, where you invite your friends and then simply fill any vacant spots with this means of player search. And if you're not assembling a team but want to show you're waiting to be recruited like this, then you search a game normally, but choose you want to be recruited like this.