While I'd love to use the new 4e FR, I positively will not simply because I've detested every actual change (as opposed to publication of new setting material detailing existing facts) made to the setting pretty much since FR gray box Day One. if they release a book for it, and I can get over the silly names, I'll go with Greyhawk and start the campaign with T1 Village of Hommlet just for nostalgia value.
Eberron in 4e sounds like fun, but I'd really have to rethink my gaming style (I tend to beat D&D into conforming to high fantasy and S&S archetypes rather than taking the game's underlying assumptions and running with them).
My guess is that for an experienced DM (which I believe you probably are, given your posts about the Hyborian APs you've run), it'd be easiest just to build a setting out of the 4e "implied setting" they're already giving us. All this stuff with Points of Light, a sample starting town, dragonborn, human, and tiefling imperial legacies, the eladrin-Feywild connection, and the new planes actually pretty much constitutes the bare bones of a brand new setting on its own.
As for me: I'll probably do what I've done with every new edition from 2e on: Reboot with the FR gray box at the end of 1356 DR (the beginning of the 1e setting timeline), incorporating any useful new FR material that would adds to the setting without generating a proliferation of new high-level NPCs, a severe retcon, or an RSE (Lost Empires of Faerun, Serpent Kingdoms, and Power of Faerun are my 3e favorites in this regard). FR is a huge enough world that I don't see any problems making the game radically different simply by choosing a different starting point. If I want "points of light," I'll go with the Savage North, the Western Heartlands, the Moonsea, the Vast, or the Bloodstone Lands. Maybe kick the game off in Neverwinter or Baldur's Gate for the benefit of new gamers who are transferring from those wonderful gateway drug CRPGs.