From appearances and specifications (and name), the S121 will be based on the 10.2″ Asus Eee PC S101, which is considered a high-end device.
From photos that SlashGear has posted, the keyboard looks quite a bit bigger. It’s an elegant design.
Interestingly enough, it has a VGA out instead of HDMI. Something in this size and probably price range (SlashGear thinks around $800 based on S101), I would have almost expected HDMI. No word on what features from the S101 will be included, as well as pricing and availability.