This is an interesting idea. Though I think, copy, cut and paste usually imply no changes to the content being moved. This is not possible to achieve in Everdo, because not every class of items can exist in every list. So “copy>paste” becomes really “copy > coerce into new class > paste”.
Also the current drag and drop between lists is different for each specific list. For example dragging an item from anywhere to Focus will only set the Focus flag and not change the actual list of the item. How would that work with copy/cut/paste? Tag-based lists are like this as well. In other words, many current drag actions will simply do nothing in many cases where doing nothing makes sense, but I would expect Ctrl+c/Ctrl-v to do something every time.