Indy himself confirms story 5 is set!

From ComingSoon.net;

"Harrison Ford tells the BBC that there's a storyline for the fifth Indiana Jones film. The actor, Steven Spielberg and George Lucas have come up with a rough outline for the follow-up to Indiana Jones and the Kingdom of the Crystal Skull.

'Steven and George and I are sort of agreed on a germ of an idea and we're seeing what comes of it.'

He added that, despite coming up with an idea for the movie, people won't see the movie for some time.

'The process works like this,' he said. 'We come to some basic agreement and then George goes away for a long time and works on it. Then Steven and I get it in some form, some embryonic form. Then if we like it we start working with George on it and at some point down the line it's ready and we do it.'

Kingdom of the Crystal Skull earned $786.6 million worldwide."