Conditional checkout attributes
This was mentioned here, but I don't see a work item.
I think conditions (requirements) could be handled similar to the way they are for Discounts. (Maybe the requirements plugins could be used by both.)
It's possible that above would be used instead of this "Accept negative discounts"
P.S. Checkout Attribute radio buttons look a bit crowded. I've added this style to add a margin to left of button
.order-summary-content .checkout-attributes input[type="radio"]{margin-left:10px}