I'm not sure supply will remain constant, but given that there are forces in both directions, I can see why coolharvard comes to that conclusion.
Western universities are under increasing financial pressure, which may well lead to a decrease in places. But there is the opportunity for them to deliver courses that are both cheaper and more popular. AKA dumber courses with more girls on them. Not all are dumber, maths can be taught relatively cheaply, and the dumbing down of CompSci courses has actually made them very cheap to deliver.
So I expect the net result of this to be more places available at most universities, especially on courses like MFEs where the marginal cost of teaching a student is very low (unlike experimental sciences), but the price is high.
Some may cut numbers to hold quality, but that's a hard line to hold. My old school's Chemistry department tried that, it is not there anymore...
The silent giant here is India.
Although the average Indian education is little better than that of an American evangelical, their IITs are already good and with an increasing % of excellent.
Typically they already teach in English, indeed a good number speak in a form of BBC English which is posher than mine.
Also, they do first world stuff like build nuclear reactors and missions to the Moon, they have a growing manufacturing sector thirsty for engineers and the Indian software sector is truly vast as well. Superstition in the USA means that medical research is moving to places that are both cheaper, and less likely to see biologists as witches.
In Indian culture, scientists are typically seen as wise and useful, in western media we are socially dysfunctional and evil.
But Indian academics are paid at a level that simply would not allow you to live in a Western country, and other resources are similarly cheap.
Already you can commission essays and coursework to be done by Indians, it's a very small step to have them as your personal tutor, who for the cost of a cheap textbook will patiently work through something hard with you until you get it right.
One day, soon, the best place on Earth, regardless of price to study some subjects will be in India, but it will also be cheaper than the worst Western place to study them.
Being a vast country, India can easily handle a serious number of students, and doesn't have the newly demented policies on harassing students seen in many Western countries.
India can do the maths of finance right now, and it would not be too hard to get some well known lecturers and practitioners. An obvious deal is to offer an older one a nice house with staff and access to really rather good affordable medical care, another area which is bringing money into India.
So compelling is the case for this, that I must question my own judgement, since my model cannot explain why it hasn't happened already.