Is it really being held off so it be be a next-gen launch title?
The tin foil hat brigade over at Rockstar NewsWire couldn't cope with the fact that Rockstar just needed a bit more time. A developer getting their timing wrong and needing more development time was too simple a reason for them, it had to be something bigger.
as Rockstar themselves said
"To those of you saying or seeing various conspiracy theories about there being some other ulterior motive for this delay, rest assured that they’re all nonsense."