This wouldn’t fix the issue, it would likely make it worse because it would be like players having their placements for the first time and they could easily manipulate their rank by throwing their 5 initial games to be placed very low. Also, with alt accounts they could do this multiple times throughout the season to further the issue.
There’s not an easy solution for fixing smurfing, but one idea I have is to look at peak performances for certain characters and like Role Queue, assign an MMR for each character that can rapidly climb with very strong performances.
An example of this could be a game where a 2500 SR smurf (who is 4000 SR on their main) plays Genji and frags out hard, getting something like 60 elims, 35 final blows, 15k damage in a 10 minute game (I made these numbers up).
This would change the Genji MMR from 2500 to something like 2700 MMR and put a soft limit at 2500 where it would be very difficult to fall below 2500 SR. After this, that player would have characters with different SR ranks (given their hidden MMR), just some examples:
Genji - 2700 SR
Soldier 76 - 2500 SR
Widowmaker - 2200 SR
This means that the player could queue at 2700 SR and have access to all their characters, or queue at 2500 SR and have Genji locked, or queue at 2200 SR and have both Genji and Soldier 76 locked. This would need to have some limit like the player MUST have 2 or 3 characters of that role (damage, tank, support), so they couldn’t queue as say, Sombra at 1100 SR if Sombra was their lowest.
This idea is probably over simplified but I think it would help the problem by having players who are very skilled at certain characters and perform well with them, rapidly have them climb closer to where they should be ranked.