Reading comprehension for some is lacking so I try to clarify my point. Sorry if that comes off as "dogged".
I should have worded my response better. I wonder what Blizzard defines as a WoW sequel? WoW is an anomaly. Never has an MMO had such huge success. As you say, "They're not going to make a successor to WoW in the form of a new MMO until WoW is either not profitable enough or they feel like it's time to move on to a brand new engine and platform".
So what do they do? Just keep releasing xpacs until they bleed all subscribers? Each new xpac, since wotlk, is a net loss of players. They have to market this as a reset. The need new and returning customers. They need this xpac to be different. So we get a lot of features that we would get in a WoW2, and it explains why Blizzards is making the decisions they are making.
We probably won't see a 5.5 and have SoO for 1+ year. They are putting all hope into 6.0 to pull back players.
I'm not saying I like what we are getting as a WoW2. I'm just saying this is what a WoW2 looks like. If WoW stays popular, in 10 more years, we will have another reset like this. Everyone will get a free Level 150, and the xpac will be the price of a full game.