Seth Godin talks about the failure of Song in terms of Delta not living up to the reality of copying JetBlue. As Diego Rodriguez notes, Goldin says it was all about an ill-fated attempt to tell customers that a brand is what Delta said it was, not the product itself defining the brand.
Yet my experience on Song flying down to visit the folks in Florida was always very good. Perhaps not JetBlue-ish but certainly a lot better than the usual Big Airline experience. Better food, much nicer service, more casual, more comfortable. So Delta is ending an experiment in a new product that was superior to its old, established product--the "Delta experience." Perhaps it will take the lessons learned in Song and apply them to the mother-ship, as it promises.
But many years ago, General Motors did a similar thing with Saturn. It launched a separate autonomous division, that built a high-quality car that customers just loved. The Saturn wasn't the most technologically advanced car but the service was the most customer-centric of all the GM divisions. So GM did what big corporations often do-- it starved Saturn of funding, poured its money into other things and, in the end, absorbed Saturn back into the bureaucracy without taking much of the Saturn DNA. Instead of Saturn remaking GM, GM remade Saturn and pretty much crushed its first new brand in decades.
Perhaps Delta will not follow GM's example. Perhaps Song is not another Saturn. Perhaps companies can really learn from one another's mistakes.