The official World of Warcraft forum website is littered with a lot of discussions involving the possibility of Blizzard opening a new realm any time soon.

Community Manager Drysc picked up the thread and provided some light into the matter. According to him, a new realm is not currently needed as Blizzard has been very successful with free transfers and the continued use of the "Recommended tag".

Drysc added that one good example of this improvement lies in the The Forgotten Coast realm.

The forum administrator also added that while it is true that some realms remain low-populated, there are only a few of them left and that Blizzard is always looking for ways to improve their condition. Drysc commented further:

I think it's easy to experience some lack of interaction at some point, maybe have been looking at the user-submitted skewed population data on some website, and jump to a conclusion that there's a correlation.

In actuality, it's just that no one wants to run that one non-heroic with you, there's plenty of people playing though.