It only has 1 SSD slot, the 15.6" version at least. I just got done upgrading the 512 GB SSD to a 2 TB SSD and it's an even better laptop now! I'd assume the 13" has the same amount of slots.
The Ion must have a different motherboard. The Ion only has 1 of 2 RAM slots soldered in as well so you can stick in another RAM stick if you want to.