This weekend the possibility of capital controls being implemented by US banks has been raised in a few places. The Hugh Hendry video is a topic here on SN

Is this a realistic threat?

I doubt it, but US banks have issues that can't be fixed. While financial media continue to push the idea that the US government should guarantee bank deposits, that supposed solution fully socializes the financial system while failing to solve the problem. Deposits will continue to drain as people buy treasuries either directly or through money markets to get a more reasonable yield. The government can't solve that problem unless drastic rate cuts are implemented immediately.

That seems a more likely outcome to me than capital controls. The Cypress solution seems drastic, as it would permanently destroy what's left of worldwide trust in the US dollar.