An all-mid mode without the random would be kinda nice
When you think about it, ARAM amounts to a teamfight simulator. This is neat.
What's not neat is when it has the infuriating ability to stick you on a pseudo-random (read: bizarrely weighted, not really random - seriously, how many times do we need to see
or
) selection of champs that you, in all likelihood, don't like or don't know how to play effectively, making the game effectively decided in champ select.
This same mode, a one-lane teamfight all the way to the nexus, would be really cool if you could pick your champs (or at least ban champs). You'd then have a mode you could actually practice your favorite champion's teamfighting skills in!
Better yet, all the code for this exists in the client (since you can make customs on howling abyss), so it would amount to creation of a new queue, nothing more.