If I may ask, what have Karn or Sorin decks done during playtesting to call for banning?

I take back some of what I said. Monoxidechild actually brings up a good point... In regular Commander, one's general can steal another's general. What difference does it make for a planeswalker to do it to another? EDH also has commanders with effects that can easily kill other commanders and I don't think any PW is broken to the extent of Griselbrand or Emrakul to be able to be banned. Hell, look at Edric, Spymaster of Trest . He garners lots of advantage by turn 3+. Karn can go off just as early with a god hand and how often do those happen? Besides, EDH is a political game; the person with the most board presence usually ends up having 3+ other people trying to rip at his/her throat, and that fact sort of balances the game out, which explains why Edric/Zur/Derevi are all legal in regular EDH but banned in duel commander.

I agree with banning Sorin Markov and Karn Liberated . Sorin can single handed bring one opponent down to 10 life, and given multiple recastings will do the same to rest of them. Karn is a little less in my mind, but a commander that can restart the game and exile at the rate he does seems like a bit much. In that sense, I would consider banning Garruk, Apex Predator , he is sort of on the fence for me with the destroy target planeswalker in a planeswalker format, but he could be justifiable. Might want to ban The Chain Veil too, just because I feel like everyone will be using it.

The best place to discuss this to get more ideas and suggestions would honestly be on reddit, haha. You'd get lots of inputs from the MtG community.

A card that should be banned preemptively Gilder Bairn it would be game breaking doubling loyality counters on planeswalkers.

Gilder Bairn is only available to Kiora, the Crashing Wave decks, I won't jump on it until it becomes a problem. It's not as large of an issue as Doubling Season , and leaves a chance for an opponent to interrupt the activation.

We're also tooling over the idea of allowing Nissa Revane decks to run up to 4 copies of Nissa's Chosen . That raises her playability, and gives her more flexibility after bored wipes.

do you allow alliances to take place during the game? play field of influence or straight free-4-all?

So far it's been free for all, but I don't see why 1v1 and 2v2 aren't manageable. Shouldn't be anymore or less difficult than regular EDH.

sounds really interesting i'm trying to find a field of influence play group

Put in Vampire Hexmage cause it could kill any other planeswalker commanders.

This should have Teferi, Temporal Archmage as he is just bonkers with the The Chain Veil and your 2+ mana making rocks.