SDXC involves major revision of the data bus, I would think. Definitely, a hardware change. Expanding into the realm of much larger data storage is the way of the future. I think back to the day when I was so happy to get a deal on a new Microscience platter drive (10MB, for about $1500).
Larger capacity means overall increased capability. It also means the potential for complexities and bloatware, as Windows has experienced, as I think back to being happy with CP/M and then ZCPR3, at 4KB for the entire operating system.
Today, with that 4KB, I can hardly squeeze the album art into that space. Times have changed.