Expansion is limited to a pair of DDR3 SO-DIMM slots (16GB max), one full-size mini PCIe slot that supports mSATA SSD drives and one half-size mini PCIe slot that's perfect for WiFi and Bluetooth.
We were also shown a Tegra single-board computer measuring no larger than a single small-outline DIMM like you'd find in a modern laptop, proof that this action can be scaled way down depending on the kinds of devices manufacturers are looking to make.