While 1.9 will not be seeing a full release at Minecon, Dinnerbone went on to say that snapshots would begin during (or shortly after) Minecon, something that will likely be a relief to many. One of the larger complaints by the community has been the inability to test for bugs, but not to worry! Snapshots will be coming very soon.
If you are planning to attend Minecon, having your hands on the official guidebook will be really handy! Even if you are not going, it has a wealth of information about the convention, including exhibitors, panelists, and activities, just to name a few!
One reason cited with not releasing an entire update at a major convention was a look back to 2011, when Minecraft officially launched as 1.0 on-stage at Vegas. The number of things that could go wrong is fairly high, and it seemed more prudent to make sure 1.9 is the best it can be, and release it that way.