I am not sure what blockchain engineers have to do with selling treasury bonds. The larger issue for China is that they have to do something with their dollars. It's not feasible just to dump them.
Unfortunately (or fortunately depending on your perspective) the USAs ability to continue to borrow does not appear to be ending. It is true that so long as others will lend to you in your own reserve currency you can basically just keep borrowing. I didn't think that the US could borrow $20T but maybe we can borrow $50T or even more. It seems for the time being the sky is the limit.