Size that matters
Takashi Mochizuki from the Wall Street Journal reported through his Twitter account that the standard capacity for Nintendo Switch game cards will be around 16 GB at launch.
This does not mean that the 16 GB will be the actual size for games. There are rumors that the system will also utilize 32 GB and 64 GB for more demanding games, even going as far as 128 GB if necessary, although at a higher cost per card.
Considering games like Splatoon were 1.8 GB in size, the Switch won’t necessarily need bigger game cards at the beginning of its lifecycle. Also, the key word is “standard” capacity, which can either mean that most of the game cards will be that size, or that 16 GB is the minimum size expected.