What EA projects could grow to become megaprojects, eventually spending $100m per year?

Abstract

Ben Todd (CEO of 80,000 Hours) says “Effective altruism needs more ‘megaprojects’. Most projects in the community are designed to use up to \textasciitilde$10m per year effectively, but the increasing funding overhang means we need more projects that could deploy \textasciitilde$100m per year.“https://twitter.com/ben_j_todd/status/1423318852801290248What are some $100m projects that you think might be worth consideration?