Texas, OK or NC for sure...
One of the points made in the article, is that the U.S. is not turning out enough engineers compared to China. To make a difference, you need to build where smart workers are being produced, preferably near big university campuses. That's a big reason why Silicon Valley was successful in California (unti liberals ruined the state). So you don't just build where salaries are low.
Apple has footprints in Texas, Kentucky, NC and a few other states. Texas is probably the best bet for a Mac plant.