Since people are still debating whether international results should count in how USFS select the world team, let me bring up a very important thing: money. Competitive figure skating is hella expensive to begin with. Doing overseas competitions makes it exponentially more expensive. Even with the hosting federation paying for tickets, accommodations and food for the competitors (which I know the Japanese Federation did, I don't know if others do), they don't pay for coaches or guardians for underaged skaters. A few years back a top level US pairs skater, I believe it was Katie Orscher, outright asked for donations and broke down all the expenses that competitive skating entails. It was enormous, and the prize money and the USFS funding for top skaters don't remotely cover it, especially for pairs or ice dancing where that money is split and many expenses (like equipment) are doubled.
For poorer US skaters who desperately want to represent their country at worlds or the Olympics (you may think of the selection as strictly an exercise for spots, but to those skaters it is their dream), they and their families can look at medaling at nationals, then earning a trip to worlds or Olympics as a doable goal they can scrounge up money for. But if you add to that the requirement that they have to do well in 3 or 4 international competitions that season, many less well off skaters and their providers will just have to give up. Even now, promising and talented skaters quit because they can't afford to stay in the sport. This will make things worse.
This is far less of a problem in the Russian, Japanese and Chinese federation, where the federation garnishes most of a skater's earnings and distribute that and other money they get to all the skaters. They also exercise a great deal of control over those skaters' choice of coaches, competition and other aspects of their lives. It's a very different system from the US. Promising skaters in those countries have a shot at having all their bills taken care of (and their individual choices taken away). Unless US figure skating gets a Russian expat takeover like US gymnastics did, we're not going to have that evil socialistic system.
Until we reach a point where more skaters (say anybody who gets any international assignments) truly have all their expenses taken care of, it would be hugely unfair to make international assignments a requirement for world team selection. As if the sport needs to be even more gentrified. And if we do move to a system where skaters are funded directly by the federation, we're going to have a very different sport. Because just like Japan, China and Russia, the people who pay the bills will demand to make the decisions (that is true almost anywhere really). The US prizes rugged individuality and pulling oneself up by the bootstrap. Which is fine when applied to what amounts to a prestigious hobby like figure skating (not so fine when applied to basic necessity like healthcare GRRR). But part of respecting that individuality and helping oneself also means not putting undue burdens on the individuals. I think it's fine and fair to require that skaters to fund themselves through regional and then nationals for a shot at representing the US. But to require that they do that for one season, then spend vastly more to pass a gauntlet of international competitions? I hate it. Doesn't enough of life and society unfairly reward the rich? In the art/sport of figure skating, where talent can bloom in any of the social strata, why make it even harder for those with less means to inspire and entertain us and make us proud?