First of all the entire Enhanced Mode menu is a case of the DS running external code in the middle of a game, so that argument doesn't work.
From what the TeamCyclops guy said in the post euphemism linked, it sounds like the way they'll be implementing the screenshot thing is to dump the entire contents of VRAM (probably to the card's internal 2MB of flash rather than to the microSD card) and then processing that data the next time you boot the card to generate a BMP image of what was on the screen. If so, d33t is right, it would be a lot like the realtime save feature, but much simpler.
I don't see any real reason why they couldn't implement both of these, but we'll just have to wait and see, won't we? At this time, saying either that it positively will or won't happen is...stupid.
...word is bondage...