I wouldn't mind seeing either rebuilt.
*Helgen you could only start it after defeating Alduin
-Build one building at a time then seek out different investors who would set up different things
-You'd have to convince people to live there
- And you get a giant statue in the middle of town of you killing a dragon

(kinda like Talo but cooler)
-and you'd have to deal with a few bandit raids every once in awhile because they didn't want to get kicked out.
just a few ideas for a new DLC
for Winterhold...i have no idea how to start that one. Learn some spell to bring back the land????