What I'm seeing so far:
- Lucas is happy with the new script for Indy 4 (not sure if I should be happy or wary there. Despite recent Star Wars efforts, all of the Indy scripts have been done well, so there's some light there).
- Spielberg is still set to direct it and has War of the Worlds coming up this year in addition to a movie about the 1972 Munich Olympics terrorist crisis, tentatively titled Vengeance. 3 movies, all in the D-seat, all big-time. Spielberg doesn't play! Still a big baller 30 years after Jaws.
- No official word on the "MacGuffin", what Alfred Hitchcock called the device employed to create motivation in the story characters, e.g. secret microfilm, the Ark, Holy Grail, etc. Only official word is:
* the story is set in the 1950's
* that the Nazis will be replaced by Communists
* Lucas has mentioned that the supernatural will once again be a part of the story.
- Rumor : Natalie Portman will play Indy's daughter. I hate rumor but I'll give this one some mention due to the fact that Lucas "loves the kids" more than Trick Daddy. I could easily see him putting the daddy hat on Indy like he made him the son with Sean Connery. It's just so a Lucas move.
Then there's the long officialy acknowledged return of many familiar faces from the previous movies, including a few of Indy's femme foils. With a daughter in the mix maybe it'll be Indiana Jones and the Search for Back Child Support.
Maybe he got with the "I Love You" mascara girl from his class in Raiders....What?
Hey, if Portman is there I just wanna see her crack the whip! Just once

Personally, I can't think of what the MacGuffin for Indy4 could be. The speculation goes on from Atlantis to Stonehenge. Though I love the Atlantis myth and the Indy "Fate of Atlantis" video game (1992) is one of my all time favorites, I'm not sure if I like that idea.
Stonehenge? Maybe. I'm thinking that would be a cool puzzle guide to the main target. Like the library/tomb in Last Crusade.
One other thing. If Connery is to be included they need to move this along. The guy has the constitution of an alligator, but he's not getting any younger.
What do you think overall? And what mission could motivate Indiana Jones to still be globe-trotting in his later years?
Source http://www.theraider.net/films/indy4/index.php