What planet said in your screen capture:
"Terry, we will provide direct boot into Linux on firmware versions. Regards, Planet"
Call me overly negative, but I suspect you are reading more into that than they actually said.
They did NOT say that Android and Linux were both going to be present in the firmware (eMMC) on shipped units.
They DID say that they, "will provide direct boot into Linux on firmware versions."
All the demo versions had Linux installed. In other interviews they said they were shipping units that would dual boot Android with Linux. None of us will know exactly how that is accomplished until we (or someone) gets their devices.
My problem with having Linux on any type of sd card is the limited write capability. I know some are better than others but it just sounds problematic. I will be disappointed if that's the way they do it. (It's fine for a person to do that for themselves, of course. ) It would also make it more complicated to swap out the sd cards with your own data.