I don't think decentralization has anything to do with privacy.

But you're right, this probably is the end of human history. Almost anything is possible with technology advancing exponentially from this already-advanced point. We approach the information singularity, long before which everything about our lives will have to completely change, likely into a permanent state of flux to be able to accommodate the pace of technological advance.

Which means there probably will never be "future genealogists", unless we're talking about the very near future.