Blockchain made it to JavaOne conference this year

I attended good old JavaOne conference in San Francisco this past week.
One could see a level of interest in Blockchain technology in developer community when all Blockchain related sessions were booked weeks in advance with long waiting lists.
I attended one such session and found it to be very introductory level about European countries like Netherlands experimenting with "blockchain like" technology for storing private land ownership registry information on distributed ledger.
The problem however is that this network of nodes is private owned only by the government agencies - hence not truly a Blockchain network that could grow.
One of the technical challenges that remain to be solved is securely storing private data on public Blockchain network.