1. Approval voting becoming widely adopted. This would go a long way toward mitigating the hyper polarization in politics in America (and likely elsewhere as well). Electing politicians with broader approval means legislation would likely move more quickly.
2. Moving to a Land Value Tax system in America. This would organically help us transition to a culture that builds up instead of sprawling out. This could lead to tremendous reductions in things like municipal infrastructure costs, transportation pollution, reduced mortgage/rent prices, etc.