For a game designed around characters which are incredibly unique, eg, you don't play an engineer you play Torbjorn, I think it takes away a lot that you can have multiple of them running around at the same time.
I do understand that it would be necessary in unranked games because people want to play "their" character and you can swap mid fight as well so like HotS, would need to be there.
For competitive ranked matches though I hope they prevent duplicates on the same team. I do see the issues that could be caused though if it prevented the other team to have a duplicate because of ingame switching. Though hopefully some skin or alternate color could be applied there so it doesn't look too bad.