Though I have never directed or produced a major motion picture (or anything, for that matter
) I doubt that is a factor. Given the returns on the previous 4 films (not to mention the merchandising goldmine), I think GL and SS are kind of holding all the chips. Any studio in their right fiscal mind would jump on an IJ film. In fact, their choice of studio has most likely already been made...didn't HF and Shia sign for 2 & 3 films this time out, respectively?
It's my understanding that SS has fulfilled his obligation with Paramount, though I'll be honest, I don't really know what that means for an Indy 5. To further complicate this line of reasoning, how may films did they originally contract for Indiana Jones? I used to know, but it now escapes me.