I have to agree with moa999. The GCCC 777 bus has limited stops between the airport and Broadbeach (few but short and worthwhile stops) and the light rail from Broadbeach north is about as best you can get as the traffic lights are controlled by the light rail. A tram doesn't stop, busses do!
Possibly the only benefit for a Skybus service would be directly up the motorway to more quickly service Burleigh, Mudgeeraba, Nerang , Pac. Pines and Helensvale, although I suspect it wouldn't be overly successful. As an example, to travel Airport to Nerang on a 777 and connecting bus, costs about $5. A taxi costs about $80 and an Uber is somewhere in between (roughly $45 I'd think). Where is the margin for a Skybus service? Either pax want a quick ride (taxi or Uber) or they want a cheap ride (bus), but all of them are relatively painless. The cheap ride does require connections which may (if you time it badly) be 1 hour, but it's at Pac. Fair where shops or coffee houses are plentiful to fill the time.