When two objects with borders share a side you just can't snap them to merge on the shared side, in order to get the desired effect one edge of one of the objects must be disabled, or one object must always be 1 pt larger in size, and overlap another object.
Perhaps an inspector setting for objects when enabled on selected objects this "smart" setting would include a object badge indicator.
The "smart" feature would apply smart border & corner logic to these objects whey they share common edge.
In addition if any object is set to hide, then the remaining objects should restore the borders & corners on the remaining objects.
This example below is a basic one, more items in series or arrangement become more complex as there are many more permutations of settings needed to achieve the desired results.