I asked a senior editor at Mongoose about it, and he said they had no plans. I'm trying to convince them.
I can think of many creatures* from The Road of Kings that are mentioned but aren't described in game terms. Adding a "central casting" list (like the one Vincent Darlage put up on this forum earlier) would make for a very solid book.
* Some of them are antelopes, mountain buffalo, giant bears, snow-dragons, wild Cimmerian bull, mammoths, condors, carnivorous trees, undines, ghouls of Ghulistan, cannibal pithecanthropoids, Remora, hairy humanoids, man-ape/abominable snowmen, snow leopards, yaks, dire wolves, mammoths, grey apes, ape men of Pathenia, jackals, desert wolves, vultures, water buffalo, komodo dragons, carnivorous plants, manticores, wildebeests, zebras, giraffes, stegosaur-like dragons, stegosaurian dragons resurrected by dark necromancy, flying wyverns, Valusian serpent men, saber-toothed cats, lamia, mermecolions, etc.
I don't have my books here at work, so I can't check to verify this list.