Okay, before we get into it, always remember this is datamined information from the next PTR and none of it is guaranteed to make it live. That being said, there are some interesting changes in the pipeline for tanks in patch 5.4, not the least of which is the creation of Riposte, an ability for warriors and death knights. The reason Riposte is interesting is because it seems to be a means to convert parry and dodge into critical strike, which means several things. First, you'll be less likely to stack critical strike as a tank (warriors were at least thinking about it with the change to Enrage, including Shield Slam and Devastate) and secondly, it makes those purely defensive stats work as threat generators, increased the low tank DPS of the warrior tank (and perhaps the DK tank as well, although I'd not heard any complaints about low DK tank DPS) and it must be noted, is not an ability that druid, paladin or monk tanks will be getting.
I find this very interesting, especially combined with the changes to Dark Command, Reckoning, Growl and Taunt. All of these abilities will now not only force a target to attack the tank in question, but will also increase her threat by 200% for 3 seconds. This means that, even if you are tanking a boss or mob that you already have threat on, these four abilities will still increase your threat overall when used, meaning that if you hit a taunt while tanking it will still have a positive effect on your threat. It's worth noting that hunter pet Growl works exactly the same - hunter pets will also get the extra 200% threat over the three seconds.
We're clearly not even remotely done with tweaks and fixes in patch 5.4, but by themselves these changes suggest that tanking is definitely going to see its fair share. The change to taunts is the biggest change to how taunting works that has ever happened, and the inclusion of Riposte goes one step further towards making avoidance also provide threat.