Friendships! They’re probably spectacular. Would you like to have some in World of Warcraft? The designers would like for you to have them, which is why the team has finished a comprehensive study of every realm’s population in WoW and is now planning to start up a fresh series of realm connections over the next 2-3 months, with a few low-population realms each week getting the connected treatment during regular maintenance hours.
The important thing to note is the difference here between cross-realm zoning and connected realms; connected realms are what allow two different servers to trade, join guilds, add to friend lists, and so forth, while you can always party up with people regardless of realm connections. The result will be that these serve as server merges that really aren’t, since no one loses a server or name. Which is probably for the best, since at this point there’s no indication of which servers will be linked up and where.