Hunter is not "grandstanding" at all, nor is this some desperation ploy, as you claim. Perhaps the most outrageous fact about Hillary is that she is a paid stooge of a Communist world power, our biggest rival for world power. Romney will never be able to exploit that issue, because he's part of that problem also. So it's a very valid attack by Hunter; the GOP shouldn't throw away a major issue by nominating another globalist jerk.
Also, this is not some issue Hunter has just started to "ride," as Romney does with all his current new-found positions. Hunter has been trying to draw attention to the threat from China for years.