One idea we’re considering is to delay opening Mogu’shan Vaults until a week or so after the expansion’s release, similar to how we’ve always handled the start of the PvP season
Mists of Pandaria will also include two other raid zones, which we plan to make available a few weeks after Mogu’shan Vaults: the Heart of the Fear and Terrace of Endless Spring.
...I think that this is a good thing as long as they don't do something stupid like lock out heroic Vaults until people clear normal Terrace, like they did the last time they gated a raid release (ICC.) It makes marathoning through the leveling/5-man phase less important to the tier's progression race.
And as a general rule, I think that anything that makes progression less about time investment and more about skill (that can't be circumvented simply by upping the time investment even more, ie attempt limits in LK) is a good thing.