Qantas did this in the late ‘90s and early 2000s. It was called CityFlyer and it involved mainly 767s every half hour between SYD- MEL for most of the day. Then came Virgin Blue which killed off Ansett. Then Qantas created Jetstar to ensure Virgin Blue didn’t get too big for its boots. Now Qantas sends 737s every half hour for most of the day and Jetstar sends A320s some of the day. They could get rid of Jetstar and introduce 140 ‘Jetstar class’ tickets on a mainline widebody and decrease the SYD- MEL traffic by about 20%. Probably make just as much money too. Of course, they’d need to invest in mainline to do it.