Of course there will be movies 4-6. Some of you think that there will be only one movie with older Indy? I don't think so. And I don't believe Marshall anymore, he's lying SoB ;>.
IMO it just looks stupid:
I-III -> about 38-40 year old Indy
IV -> about 58-60 year old Indy ??? naaah After 20 year of waiting only 1 movie? Naaah. Ford's career needs a big boost, because in last 10 years he played in really shi**y films.
So:
IV-VI -> YES ;]