Today's China is really a former multi-ethnic empire trying to redefine itself as a multi-ethnic nation. Benedict Anderson said as much in his 1991 classic Imagined Communities.
That's a very good summary of the situation. The only caveat is that this doesn't make the concept of China more "artificial" than any other national concept. Benedict Anderson's point in this classic was that *all* nations do this, and the concept of a "natural nation" is an artificial concept in itself. (I believe he used the example of Indonesia.)
Also, I would argue that China has largely suceeded in defining itself as a multi-ethnic nation, where success is defined in creating a national concept that is accepted by most of the polity. Certainly more successful than the Habsburgs, the Ottomans, or the Romanovs. It is interesting that when you list the major powers of the 21st century (the United States, China, India, Europe) all of them have had the challenge of creating a multi-ethnic national concept.
The other point is that the concept of "Han ethnicity" is itself a very interesting "artificial construction." The differences between different groups of "Han Chinese" are easily as great as those between different groups of Europeans. I think this accounts for the instinctive negative reaction that Chinese have toward challenges toward national unity. Because the idea of "Han ethnicity" is as much a construction as "Chinese nationhood" and effort to define China in ethnic terms is going to set up with a lot of small states the size of provinces.