thanks for giving this a shot.
If anyone would want to finish this. It is possile to do but requires so many workaround that its not worth to me. Will explain:
1. either make backpack as a cloak model (which doesnt look very well when moving really)
2. or make a custom content base cloak with model type 0 (that is image selected) but there raises an issue with the cloak 1 showing up whenever you equip this item (this can be workarounded though) and then apply backpack as a wing or vfx
then to make it container either
1. nwncx modification that will move the "open container" into 9' clocks
2. cast spell: unique power which will create an invisible creature, load items from database to her and open her inventory to pc, then with OnAcquire save each item added removed to database and probably limit number of items that can be there