ARM, Freescale and Nordic Semiconductor are partners of the project. While the chip in the photo appears to be Atmel (my eyesight may be failing me here), the material seems to suggest that the design is still being worked out, so an ARM device seems likely.
Fingers crossed.
As much good as Arduino has done for the Maker community, the AVR architecture is outdated.
While the Arduino did great things, I don't really see much point in continuing with 8-bit MCUs as hobbyist platforms. ST's Nucleo boards, for example, are far more powerful and very cheap at only $10. They also support the mbed platform with its online compiler, which makes it pretty easy to get started with. There's still a lot of room for improvement in the software, though.