I would honestly love it if it was set in 'post End Times where the End Times never happened' because all the overpowered rubbish that came with it would disappear, but I certainly don't think this is likely as GW still referred to how Archaon destroyed the Old World in the announcement article on Warhammer Community, meaning they're likely going to keep that all in the storyline.
Therefore, I voted 'During the time of non-End Times Warhammer Fantasy', as it is the one of the two most likely outcomes that I most certainly prefer - I have always enjoyed Warhammer Fantasy as it was, before all the the silly lore changes and massive, overpowered stuff that came with the End Times, and setting it at this time would avoid that stuff coming into it without going so far as retconning Skeletal Pope Nagash and the other End Times stuff that GW have grown to like (he just won't be present in the game as he hadn't arisen yet). Also this is the time period that Warhammer: Total War 1 and 2 are set in, and if it's going to be designed to appeal to the Warhammer: Total War players, it would make the most sense that it would be set around this time.
Time of Legends would certainly be fun because you could have armies like human Nehekharans and young Nagash's undead, but at the same time as
@NIGHTBRINGER says, you would lose many characters of the younger races, possibly even some of the younger races themselves if you go particularly far back in time. Time of Legends would also look pretty different to Warhammer: Total War and would not be as attractive to that potential playerbase (one of the two that GW are trying to attract with this). However, this would allow new characters to come to the fore with profiles for the first time (Alcadizaar the Conqueror for Nehekharans, Gotrek Starbreaker for the Dwarfs, e.t.c).
Also
@NIGHTBRINGER, you might want to change the thread title from 'The Old Word' to 'The Old World'!
