There’s probably going to be max 3 meta tanks once players figured out the best builds and ways to play. You’re going to get locked in 30min matches with the same tank that chose to play a hyper niche tank build on a weak hero. I suppose you can’t replace a tank with any of the other roles, even with the best perks. Also, what happens to leavers in stadium? Also, what happens if a tank is locked into a hero that just isn’t viable against the enemy teamcomp, no matter what build they try? Do you just have to throw yourself into the enemy team for 20 mins, trying the unachievable? I can already see the toxicity in this mode. Should be 6v6 so you could combo your build with your tank buddy and have a more flexible frontline. It’s going to be like playing regular 5v5, besides you can’t counterswap, you’re just countered. I’m willing to try it out but uhmm. Let me know if there’s anything I’m missing, because for me it makes no sense.
The match is cancelled without anyone losing rank except the leaver who gets leaver penalties.
There’s the mercy thing where stomps end at 3-0.
They asserted that there are items to help against counters. Such as Genji’s anti-beam oil. The only match ups that are a concern are Orisa and Reinhardt. Her build is more focused on being immortal and they giga buffed Reinhardt. It’s probably fine.
Another one is Zarya and Reinhardt, I have no idea how she is supposed to counter his shield build, but I imagine that’s more for the DPS to figure out. It did not really seem as if Genji or Mei had a shield break build, but I only glanced at Mei. Maybe she does.
And last, but certainly not least, Dva and Zarya. I have no clue what Dva gets now that I am thinking about it. I did not even bother to glance. 
I digress, it seems fine for the most part. The base game is worse.