Hi,
Well, it would be possible to add that capability with a plugin yes. However, the way I see it, it's not simple. It would require developping a specific interface to be able to modify the product elements in the cart (to handle characteristics, options, custom item fields, etc).
As a custom development, it would be much simpler to just handle the options, but it would still be some work. You would still need to develop a view to have the options selection interface (in a popup which would be called when clicking on an edit icon next to the product name in the cart view for example), and you would also have to handle the saving to update the product in the cart as the update functions already available are not meant to be able to modify the options of products already in the cart.