You're way too romantic. The future will be different from what we see now, because it will have different people in it. For starters: Hasidic Jews. Orthodox Jews. Evangelical Christians of many colors. Traditional, Latin-Mass Catholics. Lots and lots of all those people, because they are having buckets and buckets of children (5,6,7,8,9,10 or more per family), and so are their children, and they are sending their children to their own schools. And except for the Hasidic Jews, these groups regularly send some of their boys into the military.
And the BLMers, the AntiFags, the Feminazis, the bankers and bankerines, the druggies, hyper-preppies, the lobbyists' and politicians' children. . . if they're reproducing at all, it's by ones and twos, to divorced or never-married parents, which damages a child's ability to thrive as an adult.
Plenty of interesting foreigners will be having real numbers of children. But they are mostly of the hard-working variety, and they do tend to appreciate America.
So, America could look somewhat different, but those who "show up" for the future may be fundamentally quite similar.
It has been said that the blood of the martyrs is the seed of the church. That may become reality sooner than we care for. As Howard Stern recently said, "F... your freedom". He vocalizes what the elites are thinking.