64+GB SD cards can now be used :)
'New fact for the day: although the SD card standard says that you're meant to format 64GB+ cards with Microsoft's proprietary exFAT filesystem, and Windows won't let you format a FAT32 drive bigger than 32GB, the FAT32 standard totally does support going bigger than 32GB - all you need is a special program (link below) to do what Windows won't let you, and format it. After that, Windows is totally happy to read / write to the larger drive. And so is a Deluge.'
In other words, format the card to FAT32 using a dedicated program
Program for windows: ridgecrop.demon.co.uk/index.htm?guiformat.htm
Program for mac (not tested yet, give feedback): https://admfactory.com/how-to-format-usb-flash-drive-to-fat32-in-mac-os/