I think that every adult US citizen should get an annual share of the US GDP.

Sure thing, Sam. GDP per capita in the United States in 2016 was $52,190.90 in 2016. Debt to GDP ratio was 106.1%, or $55,374.55 per person. So. I guess we all now owe the government $3k and some. We're off to a rippin' start.

A proposal like this obviously requires a lot of new funding [1] to do at large scale, but I think we could start very small—a few hundred dollars per citizen per year—and ramp it up to a long-term target of 10-20% of GDP per year when the GDP per capita doubles.

Love it. A "few hundred dollars per citizen per year" is 96 billion dollars. Our debt to GDP ratio is now 106.7%.

I have no delusions about the challenges of such a program. There would be difficult consequences for things like immigration policy that will need a lot of discussion.

...yeah, immigration is where the problems start. Do please continue.

We’d also need to figure out rules about transferability and borrowing against this equity.

However, as the economy grows, we could imagine a world in which every American would have their basic needs guaranteed.

Why yes. Yes we could. We could also shit in one hand and wish in the other and see which fills up first.