I've been using a 64GB SDXC card with Swiss 0.3 and it seems to work okay. After re-formatting the card to FAT32, Swiss does seem to be compatible with it.
SDXC cards come formatted with an exFAT partition from the factory. Swiss hangs when trying to read the directory of an exFAT partition. Until exFAT support is added to Swiss, it should show an error message instead of hanging.
Adding exFAT support would be very useful for Swiss and other homebrew. Some SDXC-compatible devices probably expect an exFAT partition rather than FAT32. The user might want to use one large-capacity SDXC card for both GC games and their digital camera for example.
Also, you can't format partitions larger than 32GB to FAT32 in Windows without using extra software. And the maximum FAT32 cluster size is 32KB, compared to typically 128KB for exFAT. SDXC cards are likely to be optimised for being written to in 128KB-aligned 128KB chunks, meaning writing in 32KB chunks will result in poorer performance. exFAT also supports files larger than 4GB which would be useful when dumping Wii discs.
On the subject of cluster size, I tried using mkfs.vfat under Linux to format the SDXC card to FAT32, but told it the logical sector size was 4096 bytes. That resulted in a 128KB FAT32 cluster size. Unfortunately though, while I could access the card formatted that way in Linux, Windows didn't recognise it, and Swiss just showed garbage for the directory listing.
