1. Instead of 20 unrated games you are required to have 20 unrated wins. FFs don't count. Anybody who is new to the game will have to learn anyway, will be happy to play in unrated and doesn't need to be in competitive play so early.

2. In regions/times where the queue allows it, try to match people always with other people who have a similar "experience", meaning number of games played. The more games you have played in comp, the more safe it is to assume your actual rank. If you create a smurf, you would be mostly playing with other smurfs. In party situations, take the one with the fewest games as reference.

This wouldn't stop creating 2nd accounts and smurfing completely, but it makes it harder to just get into low ranks by throwing games and - as a smurf - you won't be as easily matched up with other people's mains.

I think the main problem would be higher queue times - especially in regions with a lower player base. I'm playing on EU and usually only wait 1 minute for a game - I am perfectly fine with waiting 5-10 minutes if that means playing against other people on my actual level. The queue can of course be dynamic, meaning the "match with same experience" is looser at 5 in morning when only few people are looking for a game.