While Blockchain may have the marketcap, my vote for SSN replacement would be the Tangle i.e. quicker, free, public/private. IOT fits right in

"keeping data synchronized between lots of different servers and processors"
In a parallel initiative, cryptocurrency Ethereum has begun work on its Casper platform meant to transition away from a 'proof of work' towards a 'proof of stake' incentive. Same problem set, but profits will go into your pocket, not corporations.