From what's been said, I think the days of massive settings with aggressive release schedules, like we saw in 2nd edition, are not in the immediate business plan. I think that they'll return, but later on down the road. It seems the AP approach is the direction they're taking for now. That said, Chris is working on revisiting one of the old settings, and coming out with a revised and updated version. My best bets would first be on Planescape, or second Spelljammer. This will probably be a major release, but unsure if it will be an AP, full splat book coverage, or a combination of the two.
5E's tone harkens back to that wonderful flavor of 2E, but with update mechanics that give the game a good flow. From all the great comments, it sounds like a lot of gamers are missing the feel those big setting releases had. I still enjoy getting out my box sets for Planescape, Dark Sun, and Spelljammer. As I look thru them, I think how great it would be to have them updated to a 5E version. Alas, I don't want to feel the pain, I just want to see the baby.