a) Is it possible to get a nanoBSD install onto the internal flash of these boxes?
Would this post from jimp eventually answer your question? eMMC on SG units
b) If so, is there a published procedure to do it? Is it complicated or easy?
I really think that only very experienced users, the development team or the guys from
netgate or pfSense shop and last but not least with hands on those boxes would be able
to draw a moderate way that is not harming the nand storage and is also running smooth.
I like the nanoBSD because I have never yet had a problem as a result of unexpected power loss.
For sure this will be related to the circumstance that the nanoBSD image is mounted "read only"
and there for it would not be something going wrong with this image in my opinion.