It seems as though this delay is not such a big deal after all, since it will amount to approximately one week – which would mean that everyone is approximately a fortnight away from the developer preview release. Apart from that, there also seems to have additional information shared, such as the core of Windows Phone 8.1 being completed today, although it is not ready for release to manufacturers (RTM) just yet.
Whatever bugs that have been discovered would be the responsibility of the Consumer Experience (CXE) team to clean them up in the course of the next two weeks, only then, will the software be made ready for manufacturers.
If all goes well, then the Windows Phone 8.1 RTM ought to arrive sometime later this April, and normally, it would take approximately a couple to three months before it arrives on Windows Phone, which would mean there is a possibility of a June or July Windows Phone 8.1 rollout to the masses. Of course, we do know that VLC is already waiting in the wings, too.