Burtman, I would disagree. I currently have 3/4 5.25 inch bays populated in my desktop, regularly populate an optical drive in other computers such as HTPC's, and even make use of 3.5 external bays, both for hotswap and even sometimes for FDD's. (Yes, floppies. Robotics and industrial systems still use them because they are much more resilient to contamination than an optical disk, other than perhaps DVD-RAM, which never caught on).
Mind you, If I were building a new computer, I would probably skip "Gaming" or "performance" cases entirely. Server chassis, or workstation, although with access to sheet metal fabrication equipment, I might be tempted to make my own. I have no illusions that I'm a typical consumer, but I'll miss the 5.25" slots. Fortunately, most manufacturers have a large backlog with them still present.