While disappointed, we can't say that we're all that surprised. After all, the construction of race-specific subspace inhibitors and defense platforms is no easy task, especially while trying to get a leg up on the hectic Vasari holiday shopping season. While we wait, a subspace transmission has been dispatched to Stardock representatives for an official word.
Update: Stardock's Brian Clair, aka Yarlen, has confirmed the delay on the game's official forum, writing that Entrenchment "will first be put through a public beta test for pre-order customers" in order to "finely hone" the expansion before it is released. He also notes that a final release date has not been set, and that it will "largely depend on beta feedback."