Why not have an optional mechanism where older cards from Wild / CL can be staked/put to work unchaining the Soul Bound cards for a set time?
The more BCX / CP staked per card the faster they unlock.
Even if implementation is after the 180-day DEC purchase window, it would be better than perma binding the cards for poorer players.
This way the Whales can pay DEC to unlock cards early and we mere mortals can also unlock our cards, but it will take longer.

I like this idea - I say this as someone who more than likely will not pay to unlock cards, but wouldn't mind staking some cards to break the "soulbound curse".