I think that the US is waiting for other mainstream countries to adopt their own digital currencies before launching the "Digital Dollar". If China takes the lead by launching its own "digital yuan" before the US starts developing the "digital dollar", then things will become fierce in the mainstream world. The US would not allow other countries to take the lead in economic superiority, leading them to adopt Blockchain technology in its entirety.
Now, the real question is when will the US become friendly towards crypto and Blockchain tech in general? As long as it imposes strict regulations against the industry, I don't see it going anywhere. Other countries like the UK, Malta, and even Japan have been extremely friendly towards crypto as they know it's the future of money. They're not as stringent as the US is, where it believes that crypto is only used for money laundering and tax evasion. If the US had an "open mind" it would realize that there's more to crypto than meets the eye. When put to good use, crypto and Blockchain technology can improve our economy like never before.
But be aware though, that if the US doesn't react quickly, the USD might lose its status as the reserve currency of the world. Only then, US' supremacy will come to an end, leaving China (or any other country) as the largest economy of the world. I hope that I'm wrong and that someday will be able to see an official announcement of the US government related to the wide-spread use of its "digital dollar" worldwide. Just my opinion