Community Manager Rygarius took to the forums today and had the following to say about the challenge mode season ending:
Quote from: Rygarius
Challenge Modes are not going away in 5.4.7. The End of Season Early Warning blog was meant to provide advance notice it will go away in a patch after 5.4.7 but prior to the Warlords of Draenor expansion.
So it’s still not known which patch will end the season, but at least you can stop stressing if you thought it was going to be in a week or two with patch 5.4.7!