Ford was great in The Force Awakens, easily the most enthusiasm I've from seen him in years.
Do I think he's still able to pull of being the lead of an Indy 5? Hard to say. All Han Solo really has to do is use a blaster and "fly" the Millennium Falcon, not really required to do the same amount of stunt-work that's required of Indy.
Still seeing Ford in The Force Awakens(which includes the movie and all the publicity leading up to it) its easily the most energetic of Ford I've seen in years. If he's able to keep much of that same energy and spirit for another movie, I can see him leading one more Indiana Jones film before inevitably passing down the Fedora to a new generation.