Here is my prediction.
PHB I (Arcane, Divine, and Martial)
1st Run Arcane Classes
-- Arcane powers / spells / rituals
1st Run Divine Classes
-- Divine powers / spells / rituals
1st Run Martial Classes
-- Martial powers
Arcane Sourcebook
2nd Run Arcane Classes (e.g. Bard = Arcane Leader; Swordmage = Arcane Defender, etc.)
-- New Arcane powers / spells / rituals
-- New Arcane Paragon Paths / Epic Destinies
-- Arcane Organizations
-- Arcane Strongholds
-- etc.
Divine Sourcebook
2nd Run Divine Classes (e.g. Spirit Shaman, etc.)
-- New Divine powers / spells / rituals
-- New Divine Paragon Paths / Epic Destinies
-- Divine Organizations
-- Churches, Temples, Shrines
-- etc.
Martial Sourcebook
2nd Run Martial Classes (e.g. Monk, etc.),
-- New Martial powers
-- New Arcane Paragon Paths / Epic Destinies
-- Martial Organizations
-- Strongholds, Guildhalls, etc.
-- etc.
Tome of Treasures I
New Arcane, Divine and Martial Magic items.
PHB II (Primal, Psionic, Shadow)
1st Run Primal Classes (Barbarian, Druid, Sorcerer, etc.)
-- Primal powers / spells / rituals
1st Psionic Classes (Ardent, Psychic Warrior, Lurk [or other striker variant], Psion)
-- Psionic powers / spells / rituals
1st Run Shadow Classes (Beguiler, Dread Necormancer, Shadowcaster)
-- Shadow powers / spells / rituals
Primal Sourcebook
2nd Run Primal Classes
-- New Primal powers / spells / rituals
-- New Primal Paragon Paths / Epic Destinies
-- Primal Organizations
-- Primal Places of Powers
-- etc.
Psionic Sourcebook
2nd Run Psionic Classes
-- New Psionic powers / spells / rituals
-- New Psionic Paragon Paths / Epic Destinies
-- Psionic Organizations
-- Psionic Places of Power
-- etc.
Shadow Sourcebook
2nd Run Shadow Classes
-- New Shadow powers / spells / rituals
-- New Shadow Paragon Paths / Epic Destinies
-- Shadow Organizations
-- Shadow Places of Power
-- etc.
Tome of Treasures II
New Primal, Psionic and Shadow Magic items.