Ask HN: What is the optimal consensus algorithm for a global currency?

GLOBAL CURRENCY REQUIREMENTS: (1) Medium of exchange; (2) Unit of account; (3) Store of value; (4) Global adoption; (5) Efficiency.

CONSENSUS ALGORITHMS (a brief overview): Each node in a peer-to-peer network stores a full and up-to-date copy of the entire ledger. Every proposed local addition to the ledger by network participants is communicated across the network by all participants. In principle, nodes collectively attempt to validate the addition through an algorithmic consensus mechanism. If validation is accepted, the new addition is added to all ledgers to ensure data consistency across the entire network. Examples of consensus algorithms: proof-of-work (bitcoin) and proof-of-stake (ethereum).

QUESTION: What might improve or replace existing consensus algorithms? What are the technical constraints? What is the optimal consensus algorithm for a global currency?