The time limit would drop as low as 140 minutes, compared with the current window of 330 minutes, a source familiar with the plans said.
That's going to really limit them across the Pacific - 140 won't get you from the US mainland to Hawaii - and will similarly limit other southerly Pacific routes.
Between mainland US and Asia goes up along the Alaska coast and then down along Siberia - alternates are available (assuming the weather cooperates) so that should still be OK...