While I love both Spelljammer and Planescape, unfortunately, I don't see this as anything to get excited about.
It's clear we're not getting setting books. They make it pretty clear with the CoS comparison that any fleshing out of the setting will be minimal in nature, and that it'll be rooted in FR.
Also, Spelljammer (and any seafaring D&D game in general) needs good ship-to-ship combat rules. The closest thing we've gotten so far to a battlesystem that layers over the existing D&D game is the mass combat rules, and those are nothing to write home about.
Also, I have no love at all for Dark Sun. I tried it once, and I really didn't care for it (the only reason I bought the 4e dark sun book was for the character themes and the inherent bonuses to replace magic item bonuses). Dark Sun's just not my cup of tea, but I'm glad it exists for people who like it. That said, if Dark Sun is one of the things they're going to let us lick off their fingers then I truly hope 5e's psionics aren't the "it's like magic, but magic will always be superior" system of 3e style psionics. And nothing I've seen so far really gives me any incentive to believe it'll be anything other than that.
I'd love to see Eberron get some love, though I suspect that won't happen (even in such a limited capacity as this). If they're talking about appeal to "hardcore" fans, they may well do Greyhawk and Birthright, neither of which catch my fancy.
I mean, I hope I'm wrong. I hope we get great books that really give us what we need to play in and to run these settings (which is to say mechanical updates to things like Dragonmarks, the races of the various settings, the moon-based magic of DL, artificers, solid ship-to-ship combat rules, the domain rulership stuff I've heard about from Birthright, etc). But, you won't catch me holding my breath.
