This UHS-II SD through SATA idea needs to be explored; even if we don't want it for the internal storage, it could be good to have it on one of the external SD slots. The speed of the SD slots is likely to become the limiting factor on the Pyra (like it was on the Pandora too) since cards already exist today that are faster than that. So it would be really nice if we can get a potential factor 3 speedup in this way.
If you're going to give SD on SATA serious consideration, then take a 2nd look at:
http://www.d-broad.com/db300_eg.html
It can run TWO SD ports to the SATA connector. I.e. you could link both of the front SD ports to the SATA controller.
Booting off of an internal eMMC or microSD, those front facing ports could scream. They would still be mount/unmount capable - the system would simply see them as if they were removable hard drives.
Then we get into the hacker-fun territory. That bridge controller is also RAID capable. If someone chose to they could put two SDXC cards in, set the controller to RAID 0 or 1 and have a darn fast or failure protected 'desktop' machine. Not advisable for 'normal' users, but it'd be kind of cool 'just to do'.
I think it's still in the 'hold my beer and check this out' territory. We don't know how much work or space would be required to implement a
http://www.d-broad.com/db300_eg.html type solution. The control chip is very tiny - but I'm not sure what else on their dev board would be required in a Pyra.
Still - the thought of having two front facing 200+MB/s SD ports gives me chills.