I was on B6 231 (Salt Lake City-Long Beach, less than 2 hours) yesterday in which the IFE wasn't working for the entire plane -- they announced that everyone could get a $15 credit by calling in after the flight. I did it a couple hours after the flight and it posted today. In general I've also found that B6 is quite good about issuing compensation for non-working IFE (it's happened to me before) so I don't see any reason why you couldn't politely ask for WiFi compensation as well.