I guess one thing they could do is add a drop-down menu for pets, the way they did with children. But when they added the options for young children, they made a decision most hosts were unhappy with, by determining against our will that infants wouldn't count against the guest totals or be charged.
As it stands, I'd much prefer that they leave well enough alone here. You can charge the additional cleaning fee by requesting payment through airbnb.com/resolutions and making pre-payment of the cleaning fee a condition of admitting the pet to your home. I don't trust that any new feature would work more smoothly.