In short, the process of communication between En Masse Entertainment and Bluehole Studios means that the American localization team gets a variety of options about what to release next as content, but all of the release candidates would have major impacts on endgame items. Bluehole, in the middle of reorganization to improve its communication and deployment of updates for the American players, was unable to provide anything to serve as an interim build. The community as a whole seems to be responding positively to the humility and frankness of the letter; one could use this entire incident as a case study in improving community relations after mistakes are made, really.
Source: Official Forums; thanks to Vunak for the tip!