Seconding MerricB, I too hope that the Advanced Bestiary is more than just a big book of Templates. I like templates for some things (especially Undead, for example) but I don't get all giddy over them in general.
I hope the DM's book is far enough out that it is not too late to suggest something for it:
1) Expanded discussion of cities and their population. The DMG's section is very short on this, and serves as an OK base, but there are some things that could be better handled. Like, *IF* you choose to use Prestige Classes, how to determine their highest level & supporters. Some classes, it seems to me, would be more prevalent in smaller settlements and less so in larger; while other classes would be the reverse of that. That might also vary by culture.
2) PC Domain Management rules ? Please ? This is an area that has been done, but so far, I haven't seen it "done right". That *IS* Green Ronin's motto, right ?
Ok, in all seriousness I can hope that #1 will fit into the scope of such a project, but #2 would probably be a book all by itself... maybe the Advanced Game Master's Guide vol II ?