We must be able to take a 'stock' object - a fly - and articulate it's wings, legs, abdomen etc.
While Stager seems to be bound to serve the needs of 'static still-life' art making, it is nonetheless crucial that it provide animation-like control over a models constituent parts - the wings must articulate. The entire object needs to be constructed with correct rotation axies so that the model isn't just a grouped collection of parts but a hirerarchal system.
Rarely is a detailed model in anything but an ordinary 'pose.' And, rarely is this pose particularly expressive. Without this capability, it will be difficult to wring expression from our $20 models.
Ask an animator.