Rumor: Nintendo Switch Will Support Micro SDXC Cards Up To 128GB In Capacity

[burninmylight]

Miyamotoo said:
People need to realise that 3DS "officially" supports max 32GB MicroSD SDXC but in reality its suport even 128GB when you format card to FAT32, So same thing will be for Switch, oficaly 128GB but formated to FAT32 you will be able to use 1TB MicroSD.

That's assuming that Nintendo will continue to use FAT32. FAT32 has a 4GB-per-file limit, so it will likely exFAT instead, which can handle much, much larger file and volume capacities.