Opening new realms is based on population on existing realms and expected population increase in the time ahead. We aim for a thriving population on all realms, adjusting this with migration and the Recommended tags. As long as the majority of the fairly new realms of a given type has the Recommended tag we generally do not consider opening new realms of the type.
Opening new realms is not based on whether we expect a new realm to fill up quickly, i.e. "popular request" is not considered a main argument for opening new realms.
Additionally, the argument of "ganking" making older PvP realms being unsuitable for starting new characters is not weighted heavily. This is the nature of any realm with a PvP rule set, including any "fresh" realm within a month. If this was to be a factor in considering new realms we would need to open PvP realms every month resulting in a large number of very empty realms. And opening new realms then merging low populated ones in a never-ending cycle is not considered a good solution to a problem that can be avoided altogether.
Vaneras - Basically what this means is that new realms will be opened when they are needed and not when they are wanted by players only.