Well it happened even sooner than we anticipated. The new United States Post Office opens today (May 20th) at 9am on the 27th Street side of the Grand Madison building (225 5th Avenue) just a block up from Madison Square Park. This should add some convenience for the Madison Square Park, Flatiron, and Nomad areas for your postal needs.
Interestingly, they are calling it the Greeley Square Post Office, which tells us that technically this is a replacement for the somewhat secret small post office that was at 39 West 31st Street (between Broadway and 5th Avenue). We assume they are permanently closing that location.