A BNet can be active and valid, but not have any WoW licenses attached to it. You won't be able to move a character to that account until you have a WoW license with an active subscription attached to it. I know you can transfer characters off of an inactive account, but I don't know if you can transfer them to an inactive account.
And yes, you can put heirlooms on a character and move the heirlooms over, but you're "taking" them from your current BNet account by doing it that way, so if you don't have a copy (and need one) then you're SOL. I have no idea how the system is going to work come 6.1, but I doubt they're going to just let people pull heirlooms out of the heirloom pane and move them to other accounts. The heirlooms will likely be removed from the character upon transfer, but we can dream.
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