Having ranked Arams would be more to luck than anything duo to the fact that its all random champions. Also, you'd have to disable the ability to get free to plays when you went into Ranked and I'm not sure Riot would do that. Same issue with Dominion really, you can ban out the op champions like Yi and Teemo but its still all about luck, especially in solo Q with those type of ranked games because of your team comp and who wants to go where and such. You don't get a lot of teamfights in Dominion and in Aram its all about luck on who has what champion. The thing is with Aram its one straight lane, champions like Lux, Ezreal, Draven, Nidalee, Ashe, Blitz, Ahri, Corki, etc, etc, are all pretty op in Aram simply because it takes no skill to aim their ulti's in a straight lane.
I like the idea as me and my friends do play a lot of Aram (Only occasionally Dominion if we really want to) but I can see a lot of flaws with it and I think to make it fair they would need to insta ban or remove a lot of champions from that map. 70% of Games that contain Lux or Nidalee in Aram have the winning team with the Lux or Nidalee simply because Lux fires a LAZOOOOOOR and Nidalee has a straight line to hit in a champion. Even first time players with those champions do well with them on Aram.