I love the dedication to the E6 idea but for required reading, nah.
Heh, the challenge of arguing the point
I'd go further and say it's general D&D reading that should just be done. That and the Alexandrian article on Einstein being a 4th level Expert (which I think *is* E6). As a GM I'm still enjoying throwing economic realities at my 20th level party: they have a pile of adamantine daggers, enough for millions of gp, but selling them is going to be a pain: who in a medieval world could afford a million gp pile of adamantine?! (well, I know who, but I won't say here).
I'm not sure what the point of re-publishing same old same old -type critters would be. Some samples of staples, sure, along with one "big dang monster" that can serve to scare the poopies out of characters, even if it's just CR10. Unless they're original (which would be best), why waste the space?
E6 on its own could do a very short pamphlet without having to do a big reprint. Maybe one of the pathfinder chronicles books, like the guide to Absalom, with a focus on level 6 feats. Otherwise old hands (ie: people who know about E6; let's face it) will say "ew, redundant material" and go buy, like, 4e or Gurps or something.