WOTC announced on Twitter that bans for Pioneer will be happening every Monday. We knew there were going to off-cycle bans, but it looks like it's going to be weekly. Honestly, the format feel pretty stable at the moment, I don't know if any bans are even necessary right now, but it might be because everyone is brewing their own decks. I'm sure once the metagame starts to settle we'll see what actually needs to be banned.
The only thing that comes to mind at the moment is the Copy Cat combo with Saheeli and Felidar Guardian. That's just as obnoxious now as it was in Standard, and of course Oko and Teferi are pretty dominant - like they are in pretty much every format under the sun. We'll see if they get the axe right away or if the Pioneer metagame is strong enough to compete with that nonsense.