Editing to clarify: this is not a hypothetical. This is something that I've been trying to do previously and am interested in doing a better job at in the future.
I don't work in the science-fundraising space, but my gut tells me that now would be a good time to do the last option: with the Trump admin interested in trying to reduce the NIH's budget by 40%, researchers are increasingly looking to non-federal sources of money to continue doing their (expensive) research, like the private science-granting organizations mentioned above. At the same time, there's probably a lot of philanthropists who recognize how terribly shortsighted decreasing the NIH's budget is, and who are willing to contribute more to private science funders in an effort to fill the gap.
Academic research is roughly $100 billion a year in the US. A foundation with $2 trillion could support that indefinitely with the required 5% minimum distributions. By today's numbers, the seven richest Americans could fund that.
I don't know worldwide numbers, but 4x the US is usually a good rule of thumb. You would probably need the 100–150 richest people to support all academic research worldwide.
Yes, they could, by paying their taxes.
But we’ve all seen that they really don’t want to share any of their wealth for any purpose, other than propping up a geriatric orange clown that campaigned on lowering their taxes.
PS: I said their taxes, not yours. Yours are going up, they’re just called tariffs, but that’s a tax: tariffs are your money getting collected by the government.