When Soulbound cards were announced there were always talks that they could be unlockable, in the future. No one, at the time, thought it could be anything other than the burn value. That's a very fair situation: no DEC is ever minted with this.
2x fee to unlock, even with voucher discount, is already move expensive than it should be. I'll still vote for it because people are crazy about wanting even higher fees. Just think about 5x. There's no way anyone will ever pay $62 to unlock a GF legendary. Add all the market fees that now exist, plus the risk of not being able to sell it for enough to make a profit, and the cards are still basically Soulbound. You can buy GF legendaries for cheaper than that unlock fee from CL regular and rewards set!
The cards can't stay Soulbound forever nor can they have such a high cost that no one unlocks them. This would be very bad for any new player joining in after those cards are not being printed anymore. Even anyone joining now would be screwed out of many of them. Even players who played the whole time at lower leagues, if they eventually want to invest more and move up, would be stuck with low levels for these cards.
Would this address the ability to combine purchased unlocked cards to your locked SB card to re-bind them? Or force players to pay for unbinding in order to top off cards?
I don't know how the team is going to solve that. A good solution would be to have something like X/400 BCX unlocked and only have to pay for the remaining BCX.