Just found this at "Ain't It Cool" [Published on Monday, September 14, 2009]:
Well, rejoice. It's for real. Here's Harrison Ford talking to the French newspaper Le Figaro about the status of INDY 5:
"The story for the new Indiana Jones is in the process of taking form. Steven Spielberg, George Lucas and myself are agreed on what the fifth adventure will concern, and George is actively at work. If the script is good, I'll be very happy to put the costume on again."