They still have copies of a 2000 print limited edition book for Age of Sigmar. Considering only 2000 were available worldwide I would say that Age of Sigmar has already flopped and flopped pretty hard.
....and when was this limited edition book put on sales? ...a couple of days ago? lol.
like others said its hard to judge actual popularity based on this limited edition book. Especially when GW had released Age of Sigmar rules for free. And now they are releasing a book. Some new players might not understand that.
But then again, wood elves and dwarves limited edition books sold out before release date while Tyranids limited edition still had like 400 copeies after 3 weeks of being out.
Limited Edition or 'collectors edition' also only appeals to collectors who really identify with that army or its their favorite army.
Overall I think the age of sigmar minatures sold very well because people want to use them for other games and the mini's are priced quite cheap. Somethinkg like 2$ per mini in the set compared to like 6$ mini's from buying a box of 5 or 10 dudes.
My personal small sampling of players is that the majority are buying the mini's but not playing the game.
Which I think is what GW was going for anyway since they put almost not production effort into the rules. Its just a token rules set to get new players into wargaming and then get them into 40k.