According to Scified, at a press conference for Star Wars: The Force Awakens, Harrison revealed that David Koepp would return to script the next installment of Indiana Jones’ adventures on screen:
Ford revealed that the script for Indiana Jones 5 is still in development. This is a very early stage of development which entails forging ideas for the plot. Ford detailed that the person hired to write the script would be none other then David Koepp.
Koepp’s screenwriting work includes the incredible Jurassic Park, Mission Impossible, Spider-Man, and Indiana Jones and the Kingdom of the Crystal Skull. While I love Frank Drabont and his draft had some promise, Koepp doesn’t really get enough credit for actually making Crystal Skull into a movie that could be filmed.
If this report is accurate (Scified suggests keeping it in the rumor sphere for now and cites two Spanish language sources which means something could have been lost in translation), I think its pretty good news overall. But I would expect this film to have several writers by the time it comes out, if and when it ever does.
Updated with more confirmation:
Harrison Ford me dice que el guión de Indiana Jones 5 está en fase de desarrollo. Se está encargando David Koepp
— Antonio Martín (@MartinGuirado) December 6, 2015