Ravenloft is due for an update, I'd love to see a campaign book and a few adventures for it. The world has something of a timeless feel, and it's been a while since people have seen an official D&D product for it, so I don't think they need to do a timeskip or major overhaul of the setting. It's also by nature a mysterious and amorphous place, so they could certainly add a few new domains and villains alongside tried and true favorites if they want to spice things up and expand the IP.
The fact that it is different from what you might envision as "generic D&D" is, to my mind, a strength. The hobby is crowded with niche experiences; D&D needs to show people that it can do things besides basic sword and sorcery if it wants to expand.
Eberron is a personal favorite of mine, so I hope it gets a new release as well. On the other hand, as long as the key races and so on are detailed somewhere in some D&D product, I'd rather use my old Eberron campaign stuff (whose fluff is still as exciting as the day it was released) than have them timeskip the setting or something just to drive sales.
I think a Nentir Vale/ Points of Light expanded campaign might be nice, especially as a way to bring in 4E players. Reprint the classic encounters and scenarios, complete with dynamic terrain and enhanced rules modules for AEDU and tactical battles. Expand the setting to include more real estate and new, powerful threats. Print some backgrounds to turn your ranger into a Warden or your rogue into an Avenger. I know guys in my group who would eat that stuff up!
Finally, I know it will never happen, but I'd like to see a new setting that takes D&D in a new direction and is designed from the ground up with 5E in its bones. Maybe something that mimics the innocent adventuring charm of Avatar: the Last Airbender and other anime shows. Maybe a dark setting where scattered mortals fight a losing battle against cosmic horrors in the wake of an apocalypse. I don't care! As long as it's different! We all know that D&D can be more than kobolds and 3d10 gp (as fun as that is, occasionally), so I'd love to see some professionals dig their teeth into some challenging new places for us to roll d20s.