The Seven Ages of Magic just came to my attention, and it really fits well with a lot of things I've been recently thinking about.
I love the idea that magic flows through a world in cycles, my wife has been trying to get me to read the Wheel of Time books for over 13 years now (and I had friends who were fanatical about the series before that), I've never actually read them but I get the feeling that this is a common theme through the books.
One thing that I really like about the cosmology of this cycle is the way different forms of magic might be waxing or waning at different points of the cycle within the same world. I look specifically at the World of Darkness examples that are indicated (Wraith, Vampire, Mage, Changeling, Werewolf), each e ists at a different point because that's what those games are about. But when you look at them as a whole, magic isn't necessarily dying, its just in a state of transformation.
If I look at the landscape series I've been working on, it's generally depicted as a world where the golden age has passed, a magical war has ravaged the land and the remnants of fallen empires litter the paths of a new generation of adventurers. It seems solidly in the realm of "magical post apocalypse", but different parts of the setting are actually at different points in the cycle. Some areas have distinct ruins of a bygone age, their style of magic is no longer relevant in the world, but in other areas there are factions who still cling to the vestiges of power that have maintained their dominance, for these latter groups the apocalypse is still unfolding and there is the hope that they might survive the turning of a new age. Then there are areas where the power has laid low, perhaps hiding while more dominant groups ravaged the planes, now taking the opportunity to flourish for themselves.
As I write this, it's all feeling a bit like "Ars Magica" (not that this is a bad thing).
I've developed my own paradigm when it comes to things like this, so my own interpretation of the cycle would probably collapse down to 6 stages rather than 7, with interstitial stages between them. But generally the concept holds true, and could really work well for this setting. The mystical groups from whom powers are learnt could be young and dynamic, looking for recruits but without a lot to offer them...then as they gradually build in strength they's be more cautious about who might be added to their ranks...eventually leading to complex political struggles as they become powerhouses of the mystic community...risking collapse from within as they fall prey to hubris...this seeing a gradual decay (or spectacular fall)...before leading to a period where there is nothing...then therre is discussion of new groups to arise in their place.
There will always be struggle between conservatives and progressives, with the conservatives struggling to maintain their power and fighting to remain relevant in a changing world, while the progressives struggle to gain power and resist the urge to turn conservative once they manage to acquire it.
Enough politics, back to game design...