Other than that, power creep is always going to be a thing, regardless of the motives of the project owner.

But it is a major problem for closed source systems which can be made worse if open source methods are used on cardboard. Is someone going to want to keep playing a game when they buy some boosters but find out that some of the people they play with won't play with those cards? Even worse, there isn't a uniform way to define formats?

But the nice thing about open source is that if you don’t believe it’s a good idea, you don’t have to participate.

But no one else is participating either. There are fan made TCG's, but none of them adopted the open source model. There is one body that designs cards and I don't see that changing. Even then, the trading or collecting part of that hobby goes away; they become Living Card Games instead without the collectable nature of more traditional distribution systems