Ever since the Fox sitcom Arrested Development hit the air two years ago, critics have been begging viewers to tune in, lest the innovative program go the way of other “smart” comedies, which is to say, into the network dustbin. The show has never become a hit, though, and a third season is very much in doubt. But Fox, which has traditionally been quick to cancel low-rated programs, is taking an unusual approach to the future of Arrested, asking fans of the show to sign an online “loyalty oath” promising to watch and support the show if it is brought back.