When there is an unlimited supply of foreigners willing to work for nothing, salaries for graduate students will surely be depressed even further. I suspect they may decrease to the minimum wage. I suspect few Westerners, with much better options, would be willing to work for the minimum wage for the better part of a decade.
There may be an increase in the number of PhD graduates as a result of their cheapness. Of course, the salaries for professional researchers would then drop. Very suddenly, scientists will become a cheap commodity.
These new visas may be a good thing for business, but I fear they are a disaster for any American making a career in science.