The current restriction of ‘no duplicates’ severly limits which decks are viable. And it disproportionately hurts multi-colored decks. What if you change the restriction to “In total, your 3 decks must contain at least 30 unique cards”. All currently legal deck lists would still be valid, but it would open up many new possibilities.
Would this be a good change for the normal tournaments? or better as a separate event?
I kinda like the restriction. It forces players to be more diverse and creative in their deck construction and really scrutinizing every card to make sure it’s a perfect fit. Also prevents players from using cards that are potentially overpowered in each of their decks. I think it raises the strategic level of the game as well. Questions like is it better to include 3 copies of this card in my prime deck or should I put a single copy in each of my decks are not questions that can easily be answered.
The reason behind the current format is to force players to play different decks. While I don’t like the restriction to multi-colored decks, I think your solution could achieve the opposite.
“30 unique cards total in 3 decks” means two out of three decks can be 100% identical.
So what I suggest is this: Each deck has to contain at least 20 (21) unique cards. This way, key cards can be used in any deck, but you usually make sure to not have the same deck type twice.