Three cases:

• Move and overwrite: say moving property 'a.b.c' to 'x.y.z'
• Multiple move, last overwrite: say moving property a to b, property b to c, property c to d overwriting d
• Move to insert in array: say moving property x to 'a.3', shifting up all current elements from 3 onward. If the value being moved to is from an array, shift down that array.

Currently all of these cases can require potentially large amounts of data to be passed back and forth, when the server really has all that information already.