I think it's just Blizzard making fun of themselves at this point. Or else someone on the dev team has a scat fetish.
I'd also disagree with the assertion that the overall tone is light and silly and comical. There are comical elements and quests, definitely, but that's hardly new - since Vanilla, you knew almost guaranteed that if a Gnome was handing you a quest, it would involve comic relief in some fashion.
Burning Crusade had a theme of adventure - a new world had opened up, and while the Horde definitely got the better end of the story development, it was still an expansion of both factions travelling to Outlands to kick ass, take names, and conquer. We were on the offensive.
Wrath was, in contrast, was themed by desperation/impending disaster. The Lich King was back from his coffee break and ready to kill everyone, forcing a haphazard and hasty rush to Northrend to stop him. Still offensively-minded, but with a gloomy tinge.
Cataclysm was all about rebuilding after its titular event, change and adaptation. It shook up everything in game and out, and dealing with all the changes to the world were almost as important as stopping Deathwing and his Nefarious Evil Schemes (TM).
Now Pandaria - it's not comedy, it's tragedy. The lighthearted and silly elements are important because of how they highlight the consequences of what we're doing. Both factions are back on the offensive, but against each other, the happy panda men are caught in the middle, and we're on the verge of causing another apocalypse in the process of burning this island paradise into miserable slag. It's not nearly as upfront about its doom-and-gloom as Wrath or Cataclysm were, but it only takes a little digging to find the darkness in MoP.