The huge error they made for the setting was to do the 100-year leap going into 4e. Before that, even with edition changes and world-shattering events to mark those changes, the date in the setting only advanced 17 years, from 1358 DR to 1375 DR, so much of the fluff information from even the original 1e Gray Box was for the most part still relevant even in late 3e. Had they not decided to do the century leap (and, in the process, radically change the setting's geography and population twice), we could all still be using all the old campaign setting books from way back. I'm all for a mostly-fluff FRCS, just as long as the setting timeline advancement never gets such a huge skip again...
But it is a good point that a huge setting book like that might be intimidating when drawing new players to the game, so it would have to be handled in such a way that it's shown to be an optional, instead of a necessary, purchase.