The last Community Blog Topic discussed what features we wish WoW had. Many people had wishes that would be solutions for the current low population server problem. Mine was to have one free character transfer per month. Others suggested that realms be merged and there was also much talk about making WoW one giant server.
Many pointed out that my idea of free transfers would help people leave low pop realms, but everyone might move to the same popular realms that already have queues. Leaving it up to each individual player might be too haphazard a way to handle it. But there is a certain appeal to letting people chose where they want to move their characters. Perhaps the highest population servers would not be available for free transfers.
What about merging servers? One of the main problems is perception. If Blizzard decides to save low pop servers by merging them, they will be admitting two things: that Cross Realm Zones aren't working for what they're trying to do and that subscriptions are so low they have to adjust the realms accordingly. Merging servers would definitely hype up "the sky is falling" mentality.