It's been discussed before, but I don't think we'll see anything official for a while. James Jacobs has said repeatedly that the summon monster list is locked, however some new spells might offer more specialized monsters.
Of course, Bestiary 2 did sneak in a few items that you can use with the Summon Monster lists. First off, the addition of new Elementals increased the flexibility of such entries as "Elemental (Small)" -- you now have access to the Ice Elemental, etc. in Bestiary 2. In addition, the section on templates specifically mentioned that you could apply the lawful and chaotic counterparts of the celestial and fiendish templates instead of those templates for summoned animals.
So between those two items, Bestiary 2 actually did provide a considerable boost to the variety of creatures that you can summon. It just wasn't in the form of specific additions to the Summon Monster lists.
|
...In addition, the section on templates specifically mentioned that you could apply the lawful and chaotic counterparts of the celestial and fiendish templates instead of those templates for summoned animals...
It would be nice if in the future the templates were giving some flexibility. Like the archetypes, rather than a template granting energy resistance a creature may channel energy once per day, teleport once per day, or gains a 3 bloodline powers based on Cr (at 5cr 1st or 3rd), (at 11cr 9th), (15cr 15th )
As a player there's not a lot of recourse other than talking to your DM.
However, if you have any amount of faith in the CR system, you should be able to go through and pick 3-5 things at each appropriate CR and cobble together a list. If a Succubus is Summon Monster VI and CR 7, then a Theletos Aeon should be the same, right? Or at least close enough for rock and roll.