Why hasn't this happened already?
If the workers are equivalent, but much cheaper, surely everyone would do it?
The reality is that outsourcing is never a 1:1 replacement for in-house staff - regardless of where in the world the workers are based.
The attempt to arbitrage lower wages based on geography for highly skilled roles has almost invariably, over any meaningful length of time, run up against increased organizational costs and managerial overhead for all kinds of reasons. You name it.
My general impression is that it tends to work out as a "Rob Peter to pay Paul" kind of scenario - a wash or a net negative.
There are always stories where, when everything went really well for everyone involved, it worked out as an advantage, but those - in my view - are the exception to the rule.
Now Microsoft has run a training program for IBM Amazon and Dell for the first two years and, next thing you know, you are hiring inexperienced workers with different holidays, employment regulation, time zones, and primary languages to work for the same price as the college graduate in the USA.
International workers will help keep wage costs in the USA down a little. But the talent pool for developing software is still limited. Mexico and many other countries do have some excellent universities, but companies that try to hire there are going to have to contribute to the tech sector of the host country by training and hosting entry level workers. In addition, there will be demand in those countries for the workers you are training.
Finally, if you work in finance, defense, or payments processing you can expect your off-shore, near-shore workers to be limited in what they can do. You may end up having to hire workers specifically for those contracts.