This pulldown is consistent with the earlier DL talk that it would ground 4 to 6 747-400 aircraft this fall. 2 of the 744's being pulled from scheduled svc will be used to back-fill the 2 747-200B's that are being retired from their charter runs this fall.
As for the remaining 747-400's pulled, it's anyone guess as whether they're stored temporarily...Internal DL talk was that they'd go ahead with interior mods on the parked 744's and cycle them through the fall and winter, so all 16 744's were retrofitted by next summer (not talking PTV in coach). But with DL now studying the future of the 747-400 fleet, who knows!