The ArcGIS Explorer team is very close to completing ArcGIS Explorer 2500 (formerly named 2012) we have one remaining issue that we are working to resolve today. If the problem is fixed today, ArcGIS Explorer 2500 will be available for download next week. I will update this thread with the precise status when it is known.
As Joe Flannery points out, this release has been a long time coming, the team prefers to release on a 4 to 6 month cycle. For this release we leveraged new capabilities in the Esri enterprise system, and the coordination with on-going work in that system (ArcGIS Desktop, ArcGIS Server, ArcGIS online) took some extra time to synchronize.
Thanks for your patience; the next release of ArcGIS Explorer will be the best one yet.
Mark