Carenado, a major add-on aircraft developer, has announced they are going "FSX only" with all future development. See the update here.
With FSX 2 years into its cycle, and 2 years or so remaining, it is time for this and I expect over the next 6 months or so we will see more announcements like this.
FS2004 has had its day, and it was a very good day indeed. But it is time to move on.