I like the direction you're going. Yaba's going to need to think through a lot of the implications if he does decide to make the next set of reward cards soulbound.
The idea of loading DEC into a card, equal to its burn value, before it can be sold; is excellent. I'd like to see it applied to both regular and gold foil cards, even if only for consistency.
We need to be careful not to make the game too complex. Gameplay complexity is fine, but ecosystem complexity can be discouraging to the millions of people who aren't yet completely obsessed like us :)