Well, my group hasn't really been willing to give past FH attempts a shot. So, If I'm suggesting things already covered, forgive. Still, somethings I would want to see (Assuming I can peel them away from D&D ):
A study on Mythological feel. I know this might take some research that isn't too much easier than historical, but it might be nice to be able to have a few guidelines on the difference between say, a Norse like feel, or a Grecian one. The same would go for constructing settings in those and other veins.
Speaking of Mythos, don't neglect the dieties. I'll third the suggestions on including how to make a pantheon, and what degree a GM can allow divine influence, on his game world. In the magic section (And you may have already got this covered), find a way to suggest the differences between magic and miracles (if nothing else, the priest/cleric types should have certain do's and don'ts that a wizardly type wouldn't) . Most fantasy games describe only Monothesim or Polytheism as options-If you have room, mention some stuff that is in between. Make sure that we know Henotheism is not chickenworship
In the races section, if you could show the variety in each 'stereotypical' race, I'd like it. I don't mean 'Dark Elf' 'Wood elf' , so much as the difference betwen say... Sidhe, Alfar, wolf riding savages, and little guys in a tree who make cookies: All could be technically called 'elves', and a many begining GMs think the only elves are ala Tolkien (Not that there is anything wrong with that). Similiar situations for the other races.
I don't know how much "Urban" or Modern Fantasy will be covered, but both that, and a bit on 'cross worlds' fantasy might be nice. A few ponderences on the influence of technology in a Fantasy world (as well as of Fantasy in a Modern world) might be helpful.
For that matter, a discussion of Tech levels (Stone Age, Bronze Age, Iron age etc) might be good period.
If I stated anything you have already covered here publically, my apologies. It's waayy too early in the morning.