Patch 5.4 is the final raid patch for Mists of Pandaria and ends with players defeating Garrosh and setting events in motion for a new warchief. Unfortunately, we will have to wait a little bit longer to see who that will be.
The devs aren't ready to talk about any WoW 10th anniversary events yet, but they are still working on plans for it.
The team takes more of a long term view of when making changes now. They are thinking about not only the next expansion, but the one after that when they make changes.
The amount of class spells has continued to rise over the years, so Mists of Pandaria made an attempt to cut down on the excess. Future expansions will make a bigger effort to do so as well.
Adding additional spell effects for classes is nice, but it has to be balanced with adding even more visual noise to raid encounters. Bosses and player skills that are used less frequently will likely get the more impressive effects, rather than the filler spells used in rotations.
There are a few leveling areas that need stronger guards, such as around the Dark Portal in Blasted Lands.
Adding a new classes has to be done cautiously, but adding another hero class in the future is still a possibility.
Monks were not a hero class because the low level story of the Wandering Isle fit them very well, but their population is still low due to having to level them up from level 1.
WoW won't be going free to play anytime soon, as Blizzard is happy with the current business model. Even if they wanted to make it into a microtransaction based game, it couldn't be done with how gameplay works today.
The devs want people to be able to catch up faster so that they can play with friends, which is why they are testing the experience buff and other convenience items in the Blizzard store. There is no desire to move towards a pay to win style game.