Just how viable is it? I've been going through a journey of the choices, and while moonkin had crossed my mind I had the obvious thought that it's silly since the class offers so much opportunity with versatility with tank and healing. But wait a second, some groups want ranged (especially those blindly spamming "need ranged or no invite") and to be honest I've been bored of tanking since Wrath, too much management, little number crunching, and healing, while I enjoy it sometimes, it gets a bit to my nerves on extremely hard fights (especially heroic modes you have to run a lot from position to position) since it's not just hard, but also feels a bit clunky in mechanics, especially for a healer like a druid that don't have too heavy emergency heals unlike a disc priest.
I understand though gearing is an issue and I've chosen to be a cat since I enjoy it more. One will always be inferior to the other unless you are farming something after progress for months and months. Well, that problem though is there for any offspec.