In the recent Cerebrocast focused on Boom Boom, Williams admitted that she never fleshed out how the Waiting Room works, partly to leave room for other writers to interpret or add to how it works.
Jean Grey in the words of Walt Whitman, from his masterpiece Leaves of Grass, "Song of Myself" (51 and 52):
"Do I contradict myself? Very well then I contradict myself, (I am large, I contain multitudes.)"
"Failing to fetch me at first keep encouraged, Missing me one place search another, I stop somewhere waiting for you."
Maybe if we meme some lore hard enough, future writers and editors will mistake it as fact. We could all say that the Waiting Room requires an orphan to be sacrificed in order to revive someone, and 10 years later, some writer will see it on the Wiki and add it to the book.
It seems like an awful lot of effort to bring back one character.
My flag is bacon.