From the department of expectation management: This book is going to focus HEAVILY on the core races, and not so much on the other races. Just as Inner Sea Gods compiled and expanded upon the deity articles we published in Pathfinder, so will Races of the Inenr Sea compile and expand upon the earlier race books we published in the Player Companion line; things like Elves of Golarion and Dwarves of Golarion, which are close to or are now out of print and/or have some early material from 3.5 or early Golarion that wasn't quite on model with where we are right now in Golarion.
There WILL be plenty of new stuff in the book though—never fear there—but the book's purpose is not to provide hundreds of pages of content on obscure races like lashunta, catfolk, triaxians, monkey goblans, ghorans, androids, etc.. Some of those will have some info in the book, some won't... but the bulk of it will be focused on humans, elves, dwarves, halflings, half-elves, half-orcs, and gnomes.
Creatures with racial hit dice, such as dark folk, aren't appropriate player choices and won't be represented in this book at all, really.
I'm happy to see Elves and Dwarves of Golarion getting a true Pathfinder upgrade (both books are 3.5 if I'm on point). These were some of the first Pathfinder books I picked up, and I really enjoyed how the writers, designers, and editors made "Pathfinder Elves" and "Pathfinder Dwarves" unique and new to the game. I can still see the underpinnings of the races from previous versions both literary and edition-ally, but they grew so much more dynamic and unique in Pathfinder. Dwarf casters, Elf barbarians; who knew?