I think 9.1 is actually parts of 9.1 and 9.2 combined and what would be the 9.3 patch is going to be named 9.2.
THings that make me think 9.1 is a combination of 9.1 and 9.2 combine .
9.2 things
1: Flying
2: Mega Dungeon
3: Major account wide catch ups coming in 9.1.5
Also if you look at it Sylvanas would of been more fitting for a 9.2 raid kind of like Azshara in 8.2 .