So I am not a fantasy player. I was long long ago. I wanted to get back into it, but that was around the time End Times started, and so I bid my time, of which I am glad now. BUT I am looking through the Warscrolls and rules and these are my first Impressions.
A) Did no advertising. Why advertise when you have a customer base you think is going to eat this up (whether that is true or not is yet to be seen)
B) Provided the rules for free. A LOT of 40k players wouldn't have even glanced at this if it had been a pay for rule book. BUT Now tons of them are checking it out, even though they never played before. Why? Because it as of now has ZERO opportunity cost. Heck, you can even proxy the crap out of Sigmarines and Goretide Beserkers with 40k models, and if you happen to like the game, why not just pick it up, right?
BUT I digress. A fantasy realm of swords and spears has become a Steampunk Firefight.
A) These aren't the full/final rules for each race. They are just something out there so you can continue to use your armies in the mean time until the ACTUAL faction rules drop. The fact that they use the covers for the old Army Books with the old race names on this AND contain many many dead characters is proof of this.
B) They were made simply so GW could keep their promise of "You can use your old minis". These rules will be updated and replaced, and if we are to believe, the new rules will come in the box of new models. Over the course of the AoS release, you are going to see more and more of the old armies invalidated in favour of new ones. I think that all models including and after Lizardmen, especially End Times models, are safe, but anything made before that is going to slowly go the way of the dodo.