OK，here's the case.

We know that Discover has cooperated with China Unionpay and JCB. So Discover card can be used wherever China Unionpay cards and JCB cards are accepted, and vice versa. (Plus there's no foreign currency conversion fees and the rate is pretty good)

In China, the transaction fees for credit cards are much lower than most developed countries, which usually ranks from 0.15% to 1% of the total amount depending on different categories they fall in. So the credit card never offers cashback bonus or similar award points more than 0.5%, usually around 0.2-0.3%.

However, the Escape by Discover Card gives you unlimited 2% cashback(in the forms of miles) with an annual fee of $60. And I called Discover, one of the managers in some department(I forgot) confirmed that even if I use it in China, I still get the 2% cashback, as the Terms&Conditions didn't limit the countries where the card is used in order to qualify a cash back. It only excludes certain situations like cash advance and other similar behavior like writing a check.

So what we got here is that Discover company is obviously using its own money to pay for the cash back. And people who decide to make use of this loophole can legally profit from it.

The tricky thing is:
1. Chinese dollar is not freely circulated and is restricted by Chinese central banks. So the maximum foreign currency for one Chinese citizen can buy is $50K or the equivalences. (not sure the limit about foreigners, but definitely still not much). For a bigger amount, people have to use "unofficial" ways like buying U.S. dollars from export-oriented factories or private dealers, which is technically illegal but nobody really care unless you are dealing with tens of millions of dollars.
And by the way it is not plausible to exchange them in U.S. because the rate is very bad and people lose far more than 2%.

2. There's a currency conversion loss when you buy things in Chinese dollar and exchange them to U.S. dollars to pay the credit card bills. The rate in Chinese banks is about 6.340 V.S. 6.366, so there's roughly a 0.4% loss that will partly offset the 2% cash back unless you figure out some other ways.

3. It also cost about 0.1% for the wire transfer initiated in China out to banks in America and there's a cost in receiving the funds in America. You can also figure out some other ways, e.g. bring cash back to U.S. if you travel a lot.

In a nutshell, for some people, it is possible to profit from it, and I think it really depends on if you want to adventure it and if you are smart enough. This is my first post here and I hope it helps.