There has been a lot of talk lately that flying mounts will not be usable in World of Warcraft's next expansion, Wrath of the Lich King. Blizzard has stated that the use of flying mounts may be restricted until players reach level 78 or higher. The reasoning: flying mounts would allow players to bypass too much content.
Flying mounts were introduced in The Burning Crusade, WoW's first expansion, but were not accessible until players achieved level 70. Therefore, flying mounts had little to no effect on leveling speed. They served as an end game treat for players to zip around the zones in Outlands.
With another expansion in the works, Blizzard seems to be concerned that players on flying mounts would be able to just zip around from quest to quest ignoring the vast amount of content built in between. This is understandable, as Blizzard puts a lot of hard work into building their content.
As a player who does not have a flying mount, I tend to agree with Blizzard. There is an ever growing gap between the "haves" and "have nots" in WoW. Nothing would suck worse than landing on the shores of Northrend and be forced to take the hard road as players with flying mounts zip around at 2-3x your speed while skipping over annoying random aggro.
It is understandable that players with flying mounts would be upset that they have invested large amounts of time into getting something that they can no longer use. Or not use for a certain period time. In this regard, I sympathize with flying mount owners.
However, considerations have to be made. Not just for players without flying mounts, but for the design of the content. With flying mounts, the design of both the static terrain and playable content needs to branch into a third, vertical dimension. It is not feasible that Blizzard places "flying guards" over every single quest location. The question needs to be asked, what do players want Blizzard spending time on? Getting the expansion shipped or double checking the expansion for consistency with flying mounts?
Not only is there game play reasons for turning Northrend into a No Fly Zone, but there are lore reasons as well. Blizzard has already stated they will be involving the Dragonflights heavily within WotLK. So, it may turn out that players who attempt to fly over Northrend will be downed by a "sky guard" until they reach an appropriate level and can become friendly with said "sky guard".
I strongly believe that players will be far more accepting if there is a valid lore-related reason for the restriction of flight. If it turns out that Blizzard just wants to slow leveling speed, then there will be valid room for complaints. Azeroth currently doesn't allow flying mounts, but it was also built before TBC. WotLK does not have that same luxury. Players will expect more.