I would be especially cautious about how you handle mounts. To me, they're one of the worst things WoW ever did. Really consider the implications of putting not just accessible mounts in your game, but mounts period. I've talked about this before and recently, but they remove a key aspect of player power and a key reason to interact if there is a SoW-equivalent buff in the game. I would even go so far as to say that while yes, EC tunnel was built upon trade and /ooc, it was also built around newbies interacting with high level players, and that interaction was built around the SoW buff primarily.
Mounts also eliminate much of the danger in the world, which is HUGE, absolutely huge. When you can outrun sand giants and spectre trains by clicking your mount, it cheapens the impact the world can have on your character - and thus your attachment in it. And eventually, the overworld would likely become a big silent place full of players doing their own thing, in a group or solo. It will become full of people running around on mounts, not talking because there's no reason to: there's no train inc to docks, there's no Sgt. Slate to tunnel, there's no gryphon spotted at orc camp2. None of that matters because everyone can outrun them.
Please don't make that world.
