Let's start with them having their own queue.
You see they already do in ranked, flex ranked is literally for teams of 3 or more.
The reason you got a Premade.
Your match however was a normal match and there for doesn't need to be separated because well it's normals, it's meant to be more relaxed than ranked, it's meant to be a free for all mode for you to play for fun there for it doesn't need to follow the same structure as ranked does.
The suggestion they need their own queue.
While I get playing against Premades as a 5 man random team is annoying and you're unlikely to win against them you do not get a penalty for losing so it really doesn't matter.
If losing isn't your issue and simply there behavior is, then mute them. Of what they did or said violated Riots terms then report them, then move onto your next game where hopefully you will have better enemies.
I really don't think a second queue is needed for them as it is normals it really makes no difference.