Running out of fuel and forgetting to put the gear down don't seem the most obvious scenarios. An unstable approach resulting in a botched go-around, with the classic failure to push the thrust levers all the way to TOGA, and the gear selected up too early sounds at least possible, a bit like the Emirates crash in Dubai although with obvious differences. Rusty pilots and planes standing around for long periods may have contributed. In my airbus experience the aircraft does not respond well to long periods of low utilisation, and the electronics do odd things that Boeings tend not to. If the aircraft did make contact with the runway there must be witnesses, not least the survivors, so we will find out pretty soon if this scenario applies, and latest when they read out the flight recorders.