Blizzard has updated the patch 4.1 PTR notes, and they confirm that many account bound heirlooms will now bind to your Battle.net account. Here are the details:

• Many "Account Bound" heirlooms are now labeled as "Battle.net Account Bound", meaning that they can also be traded or mailed to characters that are on different World of Warcraft accounts under the same Battle.net account.
• Mail sent to characters on the same Battle.net account now arrives instantaneously, as it does for the same World of Warcraft account.
• Mailing account-bound items to characters of the opposite faction on the same Battle.net account will now correctly translate faction-specific items to their appropriate equivalent.

The notes also state that Guild Challenges are now available for testing. For more details, check out the official Guild Challenges preview.