The above tweet references a comment to the Allison Christians revelation that the U.S. Treasury has no authority to enter into IGAs.
Although I have not had time to research this specific issue, the questions it raises are so important that discussion must begin now. I have reproduced the comment in its entirety. See also the comments responding to this comment. If this is true, the effect is that:
The retirement plans of Canadian citizens who are considered to be U.S. taxpayers will be subject to taxation in both Canada and the U.S. – pure double taxation. In other words, you work you whole life for retirement only to see the plan subject to double taxation. Assuming the truth of this (and I intend to do further extensive investigation) it is absolutely essential that you renounce U.S. citizenship at the earliest possible moment. It is my sincere hope that this commenter is incorrect. But, I will find out.
I hope you are sitting down before you read this.