It's been 2 years since this discussion... but, now is almost 2019, and we have more info on the movie.
The movie will be filmed in the UK stating from April 2019, wich is less then 6 mouths away. Also, they will indeed use Harrison Ford for probably his last shot before retireing.
Also there are rumors of Atlantis being the main plot of the story. That sounds great to me. Anyways, I hope Harrison will be able to play his role well enogh so It won't be replaced. We already saw in Solo what happens when you replace Harrison Ford. While Chris Pratt would play his role well in a Indiana Jones-type movie, he will never be as good as Harrison. I think the Franchise should have this movie as it's last one, and then end. We already saw with Star Wars what happens when you keep a franchise for too long. The new movies always get bad at some point. I just hope this does not happen to Indiana Jones.