Nah. I'm pretty sure this won't get banned, or something like Zard-X would've been banned long ago. After the discussion in "On the Radar" thread, despite being powerful, Porygon-Z has weaknesses that will keep it from being broken.
1. It's frail and kinda slow before set up. With so many powerful attackers with over 90 Speed, finding opportunity to set up is very hard. The lack of resistances due to being Normal type doesn't help it either. Because of this, Porygon-Z needs Dual Screen support most of the time to be able to tank a hit and set up, unlike things like Lando I or Zard X, who can find more opportunities to set up Rock Polish/DD.
2. It can only be used once. Because of this, any bulky phazer is a legitimate check because even a Whirlwind will make it dead weight.
3. It's predictable. It can transform into any type but most of them carry BoltBeam + Conversion + Shadow Ball or Psyshock or Recover. Basically all of it's set share 2-3 moves, that's why it's predictable. Maybe people will complain more if Hidden Power is more widely used.
4. There are enough checks. LO Bisharp hurts the Ghost variant badly (Sucker Punch is a high chance to 1HKO after SR if Adamant even after +1). There's Chansey and SpDef invested Unaware Clefable as hard stops (though fall to Psyshock variants but it's rare). SpDef Heatran can phaze it. Bulky Tyranitar can wall any hit and retaliate with Crunch/Earthquake. Ferrothorn, Excadrill and Alolan Marowak checks the Thunderbolt variants.
I think those are enough points to prove that Porygon-Z isn't broken. People just scream broken because they are unprepared to deal with this thing. It's not like Landorus-I, Zard-X or Genesect, who can steamroll even prepared teams, has fewer checks and more opportunities to set up.