Sure, you need to have 111 or more life to activate it, but it should be relatively easy to pull off in Commander even with avoiding two-card combos
Im pretty sure they mean planes walkers, but what are Magic players if not pedantic
Its obviously a much less powerful card overall, and you cant just throw it into a deck with no concern for what else is in there, but its possible there is a deck built with The Cauldron of Eternity in mind and then this deck could want Gray Merchant, but it really has to be a dedicated self-mill deck for it to work, because if you cast Gray Merchant and it dies naturally (which is the most common play pattern), it doesnt work with the Cauldron unless the Cauldron isnt on the battlefield yet
Magic Online Society's website and Discord are good places to start down the player-run-events path, and Cardhoarder maintains a list of them as well, although I'm not sure all of the events listed are still active
Kykar, Winds Fury Exxaxl: Its hard to explain why I like Kykar
Considering that some of these cards are Legacy and Vintage all-stars, it only seemed right that a ban would follow up on their announcements