I think it will be zero
I get that coupon BINs & auctions had low FVF-- maybe on average less than a dollar. And I also see that coupon sellers avoided listing fees as much as possible, more so than the average seller, because of the low market value of the product... but still, to kill a whole category of your auction platform... this is going to cost eBay.
Were coupons really that much trouble for eBay?
Drop! Take Cover! Hold On! Are you ready? Be prepared, have a plan, have 3 kits (work, car & home).