Y'know what would be cool. If there were hidden plots in the rulebook for 4e.
Hear me out.
WOTC's other big RpG "Everway" came with a setting that involved mutiple worlds. And a 36 card fate deck.
There happened to be 71 worlds connected to the main world of everway.
Nothing was said explicitly, but you could guess that there was a relationship between the 72 possible fate cards (each card had a regular and reversed meaning) and the worlds of Everway, and what the "missing" card might be.
Back when 3.0 was released and Grummsh was Lawful Evil and orcs had just been changed to CE, (which was a typo) I thought it was a provocative unmentioned story. "Why is the Lawful god of orcs saddled with chaotic worshipers. What is he gonna do about that? Do they chafe under his decrees?" Lots of plot hints.
Eberron has a bit of that, with the undeveloped Mark of Death and the 13...no, 12 theme that runs through things. Put that in the core rules. Its one of the reasons Greyhawk fans have been fans for these years. "Are Tzagy, Xagy, Zagyg and Xag all related? Somehow? How?"
Do something like giving tieflings a power no actual fiend has. Then the question of their origins becomes a deep mystery.