We've decided to reverse the rule whereby valuable blocks cannot be stolen if they are part of the structure. This is now legal, but the blocks that you can steal are still limited to: Iron blocks, gold blocks, lapis blocks, diamond blocks, all ore blocks, end stone, enchanting tables, anvils, brewing stands, juke box, item frames and the items inside them.
EDIT: This includes blocks that make up beacons. If you leave an unprotected beacon in the wild, it is fair game to be stolen.
EDIT: This includes blocks that make up beacons. If you leave an unprotected beacon in the wild, it is fair game to be stolen.