I've wondered if someday the SDBs will be truly unlimited instead of capping at 1,000 stacks. My gut tells me no, because a player could just create another box if one happened to spill over.
Don't think there was ever a mention that currants would 'go away'. XP will transition to imagination, and some currants were going to be transitioned as well...but not all...
Kudos to all you crazy people who have filled an SDB or gotten over 1/2 way there...impressive...