As I mentioned on twitter...
"It would be nice if GhostDoc commented implemented interface methods with "/// <inheritdoc/>"..."
Now, I understand that this is not an official tag but it is supported by Sandcastle (which, I believe, is the tool recommended by MS). So yeah, the implementation could be a GhostDoc option which is disabled by default.
IMO, duplicating comments is like duplicating code... I really don't see myself updating comments of multiple classes that implements the same interface.
Thanks!