I don't post here often, but I have to agree with what is being said about it being a bad idea to bring back anyone.
In fact, not only should they not bring back anyone, I say they should also venture away from the tired formula that was used in Raiders, Crusade and Skull: Opening adventure -> University -> exposition -> main adventure. It's not a bad formula, but it's too repetitive now.
They could allude to the fact that Indy works at a univerity by having him start the movie on an archeaological dig with some of his students. From there, something happens that gets him whisked away onto the main adventure of the film. By doing this, we don't get the scene of Indy standing in a classroom, nor do we get any hokey scenes of Indy at home with Marion and Mutt trying to be a family man. He could refer to his family at some point in the movie, but I really don't need to see them onscreen, and they definitely should NOT tag along with him.
The fewer references to past films, the better. No arks lying around, and I don't even need to see a snake scene again. We get it, he's afraid of snakes. That doesn't have to be shoehorned into every movie-- it's really not such a fascinating fact about the character.
I also don't need to see him fondly reminiscing about the good ol' days. KOTCS already dealt with the fact that he got older, so no more trips down memory lane.
Realistically, of course, I think its a moot point, since I can't see a 5th movie ever being made. And if it IS made, I definitely can't see GL and SS not including Mutt and Marion again (especially since Harrison himself said tht he hopes the fifth movie further explores the father/son relationship.)