Berkshire Hathaway repurchased $1.2bn of its stock from a long-time shareholder in its most significant buyback ever. The company also changed the threshold for share repurchases to 120% of book value from 110% of book value, which places a floor on the stock in many ways and signals to many investors how strongly Warren Buffett feels Berkshire’s intrinsic value exceeds its stated book value. Could a shareholder dividend be next? Berkshire Hathaway Inc. (NYSE:BRK.A) (NYSE:BRK.B) currently trades at 1.17x 3Q12 book value (book value is $111,718 per A share and $74.48 per B share as of 3Q12), which is below the new level at which the company will…