Quite a good list overall, but personally I found Larry Coreia’s Dead Six to be rather boring and predictable for the most part.
Ringworld I could see as really coming off quite well if done right. Perhaps with some version of the Hobbit’s notable feet or tree-dwelling Ewok people, or a combination of the two.
Dead Six. Predictable, I can see that... But it’s still good fun and that should just about sell itself.
If they can do things like Defiance and Falling Skies, Ringworld should be easy to produce.