That's only a partial solution. It still means that new players meet established players who are playing unranked matches. The better solution is that new players play against new players and are progressively integrated into the wider matchmaking pool based upon confidence in their rating and their authenticity. Provided the matchmaking system does this then there's no need to lock new players out of ranked matches.
Require a number of completed unrated games before allowing new accounts to play rated.

Making people play 100 unrated games for each time control (...) before they're in the rating pool.
I would like that... but only because maybe then I would be finally able to find someone here to play unrated games with, without waiting a couple of geological eras in front of the screen. Personally, I think that the only rating that has value is the one acquired in official tournaments (strictly OTB ), but this is just my idea.
Pretty much the title. If you look at most other competitive games online you have to play unranked or reach a certain account level before you're allowed in the competitive pool. Making people play 100 unrated games for each time control will let the site spot cheaters before they're in the rating pool. Either that, or it should be pretty obvious very quickly if their performance jumps up 2000 points as soon as they start playing rated.
You can also use the unrated games to estimate their elo instead of putting a 2500 player in at 1200, and vice versa someone who thinks they should be 2000 when they're really 400.