Seems to me that 28nm is not important in terms of a goal, as that is a done deal. That tech should be known fairly well inside China. They should want their own fab inside China to manufacture it, and have that fab equipment to be American-free. This I think is kind of close.
Also, the Americans do not care about the 28nm, because that is how the technology market works. The older tech, although useful, do not make that much money compared to new tech. At 28nm, that is old tech, which eventually will go obsolete or go down in price so much that it comes a low profit item. So really, how much time and resources you want to waste on that or spend on that 28nm, that is up to how much money the company has to blow.
When Huawei announced they are building a fab for 45nm to be going to 28nm, that was for their own use. They were not going to make money off that investment. It was a test to see what they can do for themselves.
Note that once the Americans see the Chinese master 28nm, they probably flood the market with those chips.