Nick Lachey and Jessica Simpson revived the long-dead variety-show genre on Easter Sunday, and in the process, helped revive the Sunday fortunes of ABC. According to Nielsen, ''The Nick & Jessica Variety Hour'' drew 11.4 million viewers and was the evening's top show among 18-to-49-year-old viewers. It far outdrew the slot's usual occupant, ''Alias'' (which is averaging 8.1 million viewers), and it was the night's second most-viewed show, second only to ABC's own ''Extreme Makeover: Home Edition'' (11.7 million), which preceded it. As a result of the ''Newlyweds'' stars' success, ABC is planning another installment at Christmastime, according to the New York Daily News, with an eye toward making their ''Variety Hour'' a quarterly special. We're sure that Lou Ferrigno, the Captain and Tennille, and Reggie Jackson are lining up to be guests.