Keeping Orb Generators on cooldown, keeping ToF maximized, moving, and making the most out of Insanity without distorting your higher priorities (which is all of them) are the core challenges of Shadow this expansion. It's certainly not as hard as it has been in past expansions, but there is a lot of subtle knowledge and skills that most Shadowpriests don't make use of - and certainly the alt specs of Warlock mains are likely missing ;p
Destro and Demo take no effort, you build up power, you expend power on finishers, and they both have massive capacitors for power storage until when it is most convenient for you to use it: which means you really can't make a mistake if you tried.
Affliction is just Cataclysm Shadow priorities copied verbatim and then made much easier. You soul swap some dots onto things, you haunt things if you run out of target to swap dots to, you malefic grasp if you run out of those things, and you drain soul when things are about to die: that is the entirety of the spec.
We can talk about maintaining Haunt uptime, but that's really easier compared to our old Shadowy Empowerment which was pseudo-randomized and thus very hard to game to maximize uptime (but could be done), or we can compare it to ToF uptime - but by comparison ToF uptime is again way harder to maintain than Haunt - we have to snipe heals on low hp raid members, or do entire encounters locked in at <35% health - all you have to do for Haunt is "Do I have a shard to spare? No. Ok, then no Haunt."
In WoD they will just make Affliction into MoP Shadow, and then we will have to deal with all the Locks coming to tell us how they deserve Nobel Prizes in Science for their original work in maintaining Twist of Nether uptime, or how challenging it is to move without any spells that work on the move (WoD is removing instant spells after all).