Currently our snapping logic is doing a matching between the dragged items and all visible items in the viewport. This operation is hurting the performance because it is done on mouse move. That is why we did not included the center of the shape into the snapping.
As Francois said, currently there is no extensibility mechanism allowing customization. You should implement the whole snapping logic by you own if you want to customize it. We shall take your suggestion into consideration, estimate it, schedule it and get back to you.
the Telerik team