I think if they're going to the lengths of making a Ford starring Indy 4, I doubt very much that Lucas and Spielberg will do any more, non Ford, related cinematic adventures for Indy, and surely Ford would HAVE to be too old for an Indy 5 in 2015??
They've been very adamant throughout the development of Indy 4 that no-one else would be considered to don the fedora.
Having said that, we all know how Lucas likes to milk ideas to death it wouldn't surprise me, especially if Indy 4 is a massive hit, that we get another spin off series, maybe a different take on young Indy, or more likely, an animated series...
Dr.Sartorius said:
I think an Indiana Jones Animated Series with Harrison as the voice of Indy could be great.
Now that would be cool, an animated film even, if done well and had Harrison's voice, would be great!