Mexico has gone through the textbook demographic transition. It is possible that the country may follow Latin countries Spain and Italy and see fertility rates drop well below replacement levels and population growth diminish. This would have a significant impact on economic and cultural connections between Mexico and the USA.
What does Mexico have in common with Spain and Italy? A heavily Roman Catholic population historically, and close cultural and economic ties with countries with aging populations thatthat are below replacement levels of childbearing. It’s not unreasonable to project that Mexico’s demographic trend has a good chance of being in line with the result seen in these countries. Here are charts of the trend for each of these countries:
The key impact of significantly reduced population growth is that the need for GDP growth to simply maintain standards of living for the populace goes away. The economic pressure to migrate to find work is likely to diminish significantly. Of course, non-demographic factors could trigger significant outmigration. But the seemingliy predictable flow of people seeking work would end.