Hello.
When you specify a selector in a VisualObjectInstance object, Power BI attaches an "objects" array to the data-point's parent in the dataview, that contains the new data, rather than to the metadata object.
For example, if you're using a categorical DataView and you change the color of the second item in the first column, then categorical.categories[0] will now have an "objects" array. That "objects" array will hold an object corresponding to the VisualObjectInstance at the same index as that of the data-point in the "identity" and "values" arrays. In this example, it's categorical.categories[0].objects[1].
Note that despite the fact that the "objects" array's length property is the same as that of the "identity" and "values" arrays, it contains items only for data-points that had their properties changed.