I only play ARAM because I find Summoner's Rift too arduous for my patience and time constraints. I thoroughly enjoy ARAM but find two things about it annoying:
1) Being stuck with a champ you didn't want to play.
2) People dodging at the last moment because they got a champ they didn't want, only for the game to start before they've fully exited the client, leading to a 4 v 5 (this is becoming increasingly common).
However, I think there is a neat solution to this.
ARAM is random because historically, there was a huge gap in effectiveness between the map's best champs and worst ones. However, Riot now do champion balance updates specifically for Howling Abyss, so the gap between the best and worst winrates has closed and is likely to close further. As a result, there is no longer a necessity to balance the map with randomness, so I think there should now be an option to play on the map with a champion of your choosing (with bans, etc) rather than one that you roll for.
I don't think splitting Howling Abyss between 2 game modes would significantly affect queue times, as the division of players between the modes would be offset by an influx of players like me who want the fast pace of ARAM but with the ability to choose who we play as.
What do you think?