Importing cheap labor has been a constant throughout the countries history, look at camps of people building the railroads you’ll see lots of Chinese people etc.
How do we solve the issue of the end state, where all economies have reached our current level of advancement?
I assume we solve it, or we go extinct, and that would be an odd reason to do so after millions of years, wouldn't it?
The USA as a whole has 1.7 births per woman which is really close to the ~2.1 needed. However that isn’t evenly distributed ethic Native Hawaiian and Pacific Islander’s living in the US actually sit just above replacement rate. Give it 200 years and that may very well increase.
Really 3 kids needs to be seen as normal long term because some people just aren’t going to have any.