China is thinking of abandoning the dollar. If China creates its GovCoin and pegs the yuan to it, the yuan will become a threat to the dollar. The only monetary weapon the US has against the yuan is Bitcoin. So the US will want to maintain faith in Bitcoin
Just claiming something is not enough
It would be nice if you explained how the so-called GovCoin is going to become a threat to the US dollar. I guess you shouldn't multiply entities beyond necessity (Ockham’s Razor). In this case, your GovCoin is such a useless entity essentially. What prevents them from using their national currency as "a threat to the dollar"? I guess this coin will be a threat to the Chinese yuan itself in the first place, not the American dollar. Or do you really think that if people in China don't believe in yuan, they will all of a sudden start believing in what would be just the same yuan in disguise?
This has been done for hundreds of years. Countries have always strengthened a currency by pegging it against a stronger one. Instead of a gold or dollar standard, China might have a ChinaCoin standard. ChinaCoin may become credible, since it'd be supported by the Chinese government with its big economy
Whatever China pegs their currency to, it won't be stronger than that
If they peg the Yuan to the US dollar, it simply can't be a threat to the latter. If they peg it to gold, then more power to them. Most major currencies (like the already mentioned American dollar, Euro or Swiss franc) are by far more stable than gold (gold in comparison with them is as volatile as hell). Other than that, you can't solve a problem by relying on people who created it. Should the Chinese authorities create their own GovCoin (that's what you started with), they will abuse it in absolutely the same way they abuse the Yuan right now