I guess They shall not be able! as well as the 3dbrew team has not been able !
It's quite reasonable, but I think it is still possible. Since the 3dbrew team did not release any possible solution, at least they did not publish, the Gateway 3DS team probably have their own tricks.
Moreover, I think it's quite possible for them to break the 6.20. As they use a ds card to initialize their system, I guess the cracking point might relate to ds mode. The ds mode is already cracked, so the same mechanic should work for the later firmware, at least the firmware released before this card.