Sure, but date formatting? That's where Go is going to differentiate itself? Even though it still uses a C-like format string? This seems like exactly the kind of area where leveraging the existing conventions would be a no-brainer.
It isn't the format string syntax that is the problem that they're trying to solve. I see this as being an iterative, backwards-incompatible improvement on the existing format convention. Changes in convention don't have to be all or nothing.