The primary purpose of the Bestiary was to replace 3.5's Monster Manual. And since the 3.5 Monster Manual skewed heavily toward CRs of 10 and lower, that's just a natural result... although there is more variety in high CR options in the Pathfinder Bestiary than there were in the 3.5 Monster Manual (we have some high CR aberrations and oozes and the like, for example).
Bestiary 2 will (like the Monster Manual 2 for 3rd edition) have more high CR choices. It'll also, like all of our hardcovers, be 100% open content.
I was thinking about that. I think an interesting option was presented in one of the later MMs, in the form of more higher-level examples of current monsters. Not just the ones presented in Ecology articles, of one-off special monsters, but rather a pile of examples of a particular race for use by GMs.
Like the Goblins in RotRL, how in the Bestiary they're 1st level warriors; but if I wanted to make some Goblin Bards or Barbarians, or even an elite group of Goblin Rogues or Fighters, it might be more realistic for an adventuring party encountering a cadre of the little blighters.
I just don't know whether just having more upper-CR critters is a good idea. Like in Savage Tide's later episodes, how there was this assassin based on a demon but with two assassin levels. I mean, just two. The rest were the usual monster HD. While that's good for a foundation, I think there's a lot of things that monsters don't make up for vs. PCs unless they've got more... well, stuff going for them.
Granted, yes there should be big beasties like the Shoggoth: so glad that's a Core PF monsters, actually; and more giant scorpions and spiders and dragons and such. That makes sense, and should be that way.
But I like the idea of a base-race being, like, CR8 and then level up the more powerful options. At least for the intelligent creatures. My defense for this is that if I wanted to have Cyclopes Archmages, they by definition have to be Epic Level before I can pit them against my players *if* the base race is CR20. Since they're CR5, I can pile on some levels and have them ready to challenge the PCs in a reasonable manner.
I guess I'm thinking about the power creep that happened in 3.x, like in FR.
Then again, there is the problem of having GMs leveling up *every* monsters once the players are around 8th level.