Most foreigners in the US, not counting those from unstable war-torn countries, are not really here for "opportunity" but quality of life. True opportunity-seekers are already mostly gone (or aren't even trying to get in); there is far more opportunity elsewhere. It is losing the talented and educated, but less-driven quality-of-life seekers that will cause the bigger hit, because they staff the wealth-creating efforts started by the opportunity seekers, both native and foreign.

Most of us are here to get away from poor living standards where we come from. Clean air, good public infrastructure, national parks, very little visible poverty, low crime, no ugly slums all over the place (real downer, I can tell you that), healthy, optimistic and happy (mostly) people all around you.

Only a fraction are the entrepreneurial, driven kind that wants to pursue opportunity. Most just want a steady job, nice house and family in a nice neighborhood with a great environment and enough resources to pursue some interests and hobbies. For a lot of foreigners, merely getting here and joining the middle class used to be a satisfactory life accomplishment, and reason enough to slack off and coast (which isn't to say they stop adding value, since they have the talent and education to add value even while coasting).

When that starts becoming unreasonably hard to achieve (which is happening rapidly), the general reaction tends to be, "screw it, this is getting way too hard..."

Forget foreigners. Talented Americans are flocking to Timothy Ferriss' 4-hour work week idea and flocking to places like Bali and Thailand. You may want to track that metric: the local talent is heading elsewhere. If you're young, single and without kids, easy-going enough to be comfortable abroad, and not insane enough to join the rat race here, heading overseas may be the right move.

I am not sure visas are a good indicator. One of the few sectors that does a good job in the US is graduate education and business training. So long as basic law and order don't break down and there is no violence against foreigners, people will still see the US as a good place to get a great education, early-career business/professional training, strong international connections.

What matters is what they do after that. Do they stick around for the onerous green card process (frankly, no foreigner cares about visas... green cards are the promised golden ticket)? Or do they take Mandarin lessons and look for a Shanghai posting?

So what you want to track is the return rate after a few years on an H1B among immigrants from stable developing countries. In particular look inside large MNCs. Large multinationals are very international, with the top 100 having 60% or more of their assets abroad. As they ramp up their non-US operations and look for volunteers to go staff those other locations, you should see a steady increase in people taking those opportunities. They get near-Western salaries in gated compounds in the developing world. For many, this is a have-cake-and-eat-it-too proposition. But even in these MNCs, including the big ones that are slowly shifting their center of gravity eastwards, you mostly still need to start your career here (I know the Quora crowd is obsessed with startups, but they are not a big employer of foreigners; the vast majority of foreigners still work for the larger companies).

This has already been a growing trend with Indians in the last decade. Especially among the ones who value traditional community and family more.