For my use, I don’t much care if it is opt-in (preferred) or opt-out, as long as it is not mandatory, so I can choose what works best for my 4 sites on different hosts. I just converted an image from WebP for a friend with an older computer, and the JPEG was MUCH smaller. I would like to be able to choose for each photo, as I find that some photos are smaller in PNG vs JPEG, others JPEG is smaller.