Windows Phone 8.1 core may have been finished today28
The delay isn't all that big a deal it seems. According to Rubino, the delay will only add up to about one week, which would mean that we're about two weeks away from the developer preview release. There is also a bit more info to share that says the core of Windows Phone 8.1 was finished today, but it isn't quite ready for release to manufacturers (RTM). Rubino mentioned bugs yesterday, and now he's saying that those bugs fall under the purview of the Consumer Experience (CXE) team. They should be exterminated over the next couple weeks, and then the software will be ready for manufacturers.
If the timetable holds, it would put the Windows Phone 8.1 RTM likely in late April. The time between RTM and general availability can vary, but usually amounts to two or three months when it comes to Windows Phone. This would mean Windows Phone 8.1 could start hitting devices sometime in June or July.