One change within the existing economic system would solve all problems at the macro level (sustainability, poverty, taxes/public debt, etc.), creating a temporal space in which necessary technological changes could be brought to bear. Any nation--or group of nations, to include all nations--could adopt the paradigm to supply the economy with money (as currency).

if curious: "A Most Beneficial Economic Change" (a "2 min read" here in Medium with links to articles about the idea from various perspectives--nothing behind the paywall)