Sure they will - I just had my '16 GT hood replaced under the corrosion warranty in March. Now they DID change the warranty between '15 and '16 to be MORE inclusive - so your statement is only partly true - on a '15 you have a shorter window to get it fixed, '16+ its 8yrs/unlimited mileage I believer (maybe 5yr/unlimited) but they sure DID replace/repaint my hood under warranty.If your talking about paint bubbling, my buddy has a body shop, he says it’s aluminum oxide. Ford knows about it but they wont fix it under warranty.
Side note - its not just Ford that is having the issue, my dealer has a Dodge dealership next door and they share the body shop. When I was getting mine done the service manager stated that the Dodge cars with Alu hoods had the same issue in the same place - leading edge of the hood. He did not understand why it was happening either - the F-150 has been all Al for years and he said they don't see the problem on them.