Nintendo Switch supports all Micro SDXC memory cards, the platform holder has confirmed. In a statement to Game Informer, Nintendo said, "Switch is compatible with the SDXC standard, which supports up to 2 TB. (Note that 2 TB cards are not yet on the market, but the system will support them when they are.)"
As Nintendo notes, 2 TB cards are not yet available to purchase. In fact, it seems even 1 TB cards aren't on the market yet either. The largest commonly available SDXC card has a capacity of 512 GB, but these retail for upwards of USD $200 / £200 in their respective territories. Smaller capacity cards sell for progressively less.
It is worth noting, however, that Nintendo Switch games are not required to install to system memory--as PS4 and Xbox One games are--so the hybrid console's storage will likely not fill as fast as Sony or Microsoft's platforms unless you purchase the majority of your games digitally. Switch includes 32 GB of storage built-in, too, so you may never need to purchase additional SD cards.
Digital downloads can be large, however. The Legend of Zelda: Breath of the Wild takes up around 40 percent of Nintendo Switch's on-board memory if you download that from the Nintendo eShop.
Nintendo's previous console, the Wii U, supported external hard drive support, as does the Xbox One. PlayStation 4, meanwhile, does not support external storage, but users can replace the internal drive without violating the manufacturer's warranty. Find out how to do that here.