I am using a mixture of FR, Scarred Lands, and my own ideas. I've modified the FR some from the 4E games, with the spellplague being the result of a battle between the FR gods, another pantheon, and the primordials/demons. You can find the start of information for the campaign on my blog on this site.
I've set the world about 50 years after the world shattering events, with the idea that all these powers are unexplained and are developing as the world re-settles in place after the massive energies released into the world. NO ONE knows what all the powers are. NO ONE knows what all the options are, who the real powers in the world left are (and what new ones are rising).
Setting the time closer to the events, and stating that these powers are new and are being discovered gives you metagame explanation for introducing new powers (or limiting them).
I'm also incoprorating when the sky falls and chaositec from Monte Cook's 3E materials. Ao and other gods and primordials "fell" into the Sea of Fallen Stars, which had a very prophetic name.