We had season of discovery which was pretty cool. It was kind of a classic plus. Id like to see a different idea.
I would like to have a MoP remix style of classic. “We are teleported from the future to the past, we have to analyze the quests, dungeons, and raids for the anomalies”. They bring all of the modern classes and specs and have “temporal empowered” quests, dungeons and raids, the main villian could change things, such as releasing Cthuun before we open the gates, bringing Varian back before wrath, getting the nightborne to leave Suramar. I mean, anything would be possible. Also releasing the expanded cataclysm map without the old world revamp would be cool, think of hyjal and twilight highlands. It could still take a long time to level up. Isolated pockets of questing areas could be empowered at random for new challenges, heroic dungeons, heroic raids. And progress would be shared with retail, no more collecting certain things that you may not be able to use ever again.
You can thank the friday maintenance for this post.