So we have the 5th ed DMG on the way. I've been pluging it into the of the D&D Basic/Mystara stuff and it has been working great. It has me wandering though what are some campaigns people will rebooting? What reboots do people want to see?
I think Urban Arcana would be a keen and unexpected choice. Let's see what happens.
Dragonlance. 'nuff said
Inquistor wrote:
Planescape!!!!
I would love to see a 5th ed go at games like Dark Matter, Top Secret, Gamma World, Star Fornteirs, and perhaps some of the Amazing Engine Titles. 
First, Birthright. Second, Planescape (with Factions).
After that I'm not sure though I'd probably put Dragonlance near the bottom of my list.
I would love to see 5th ed books for Eberron and Dragonlance.
Planescape and Birthright. In that order 
Here's a thought: What if campaign settings were bundled into a book series? Take 3-4 settings, probably a mix of bigger and smaller names, and group them into one book. So Planescape/Ravenloft/Oriental Adventures in one book. Birthright/Dark Sun/Eberron in the next. Spelljammer/Dragonlance/something new in the third. Sure, these will be more abridged than a full-blown boxed set with maps, but it could work.
Each section would introduce the world, go over basic geography, tone, major history. Add some selling points for why you want to play in Dark Sun vs. Eberron vs. Dragonlance. Drop in a few appropriate optional rules, new races or subraces, a feat, maybe. This gives updated rules where needed, plus allows you to sneak in a couple settings that might be a hard sell for a big book of its own. No offense, but WotC probably bets only the 20 people who bought Birthright the last time around would be interested in a full-blown reintroduction. If it's bundled with another setting they are already interested in, people might be more likely to try it out.
You then incorporate a more in-depth description of a particular topic along with the adventures. The Red Wizards of Thay might have only had a line or two in the Settings Guide, but in the Thwart the Red Wizards adventure book, you add in the full details.
Greyhawk & Darksun
Planescape
My number one desire for a Campaign setting is very easy: Planescape.
Beyond that I'd like to see Forgotten Realms, and maybe some sort of Spell Jammer update, though I doubt the latter will happen.
I hope to see an updated Mystara campaign, with Karameikos as central for adventures with credible hooks leading to neighboring regions. I also hope to see new info on how the neighboring regions actually interact with each other. But please avoid throwing in something so big like a catalysm that induces so much changes that make everything unrecognizable.
As I think I said in another post, Planescape really gets my attention. And I would add Dark Sun =)
Greyhawk. Updating the setting and moving the timeline forward several decades or longer would be a big plus.