I might have read it here or on another forum where the idea of Indy in the sixties for the setting but adding flashbacks to adventures when he was younger. That way, the audience can be introduced to a replacement for Ford (younger Ford) and have more Indy movies with the new actor but based in the past.
If not - they can reboot the franchise and introduce a new actor then. If they do that it will give them more flexibility to move the character to present time if they want.
Would be funny in the script if Indy somehow drinks from the fountain of youth or some other type of magic and the ending is the flashback actor being Indy in the movie present time-line.........