Why not just have new accounts play 10 draft games before they can play ranked. From those 10 draft games you get a rough estimation about their skill level, and from that skill level you play your first ranked game?
Example First draft game is gold 5, after 10 draft games you become silver 3, then after 10 ranked games you are placed bronze 1
It's not a bad idea, but draft games aren't played with the same competitive intent as ranked games, so we can't guarantee that how you do in those 10 games is representative of how you'd do in Ranked. I wouldn't trust Normal data as the only way of seeding someone, but it could be part of the solution along with other info.