On Mail,

Given that they are merging realms to the extent of allowing guilds and the AH inside the newly created realms, but not forcing name changes, they're effectively implementing cross realm mail/trade/etc within those communities. It's just a question of if they'll allow it everywhere. They might hold off due to a desire to keep the economies unlinked as mail would enable a whole new metagame moving goods between realms for higher resale.