This non-suggestion doesn't fix the non-problem you think you're addressing.
First off ->* "Obviously some care would be needed in the 10-20 champion range, where the vast majority of ARAM smurfs reside"*
How do you know this? What's your source? Answer: you don't know this. My main account has ~116 champions. My second account has 45 champions. ARAM accounts do not have a fixed number of champions. Some ARAM accounts may indeed only have 10-20 champions. But not all of them. And you have no way of knowing anyway. How do you differentiate an ARAM smurf with 30 champions from a non-smurf account with 30 champions? You cannot look at individual champions alone and draw accurate conclusions.
But more to the point, if you separate matchmaking by number of champions, then -- if you're right about ARAM smurfs -- you're going to see ARAM accounts matched against recently level 30 accounts. Those recently-30 accounts may only have 10-30 champions unlocked from IP during the grind to level 30. That's not going to be very fair for the newer players.
What percentage of the ARAM playerbase has 50% champions owned? 75% 90%? Again, you don't know this. Do you match players with >75% of champions owned against other players with 100+ champions owned? What's the cut-off? Players with a large champion pool are going to experience longer queue times, just to not solve a non-problem (OMG ARAM SMORPHS). Is it fair to match a player with 60 champions unlocked against a player with 95 champions unlocked? Is a player has 40 champions unlocked, is that "too many" to be matched with the players with 10-20 champions? If 40 champions owned "too few" to be matched against players with 80 champions unlocked?
This non-suggestion doesn't solve the problem you think you're solving. Even if you match players based on champion pool, that doesn't address dodging (players are still going to dodge if they don't like the champion assigned to them, or if they think their team isn't going to work). Since there's no way to really know if a player with 25 champions owned is a smurf, or just a new(ish) player who doesn't have money to spend on RP, you can't segregate ARAM smurfs from the "general population". And while you may not care if ARAM smurf accounts have disproportionately long queue times, those players do (and Riot will too). Likewise, you can't pair up players with >100 champions unlocked with other players with >100 champions unlocked because of disproportionate queue times.
This idea doesn't fix anything. At best, it's a band-aid solution with no longer-term analysis put into it.
