Not enough time to educate them and not enough time to make the move to the legit world of legalized gambling. That's what I think atleast. Vito would have hoped to have been completely legit if the day ever came(God forbid) that Mike had to take over the 'olive oil' end of the business. Thanks to Sonny's death, Mike DID have to take over, and the Don had not yet made his move to the legit world. 'There just wasn't enough time.'
I disagree. I don't believe that Vito ever thought the HE himslef would bring the family business over to the legitimate world. I believe that he had hoped that Michael would be the son to do this, but not himself.
His saying that "There just wasn't enough time" was, in my opinion, said in regards to his not having enough time to mentor Michael in the illegitimate end of the business because Vito never intended for Michael to have to handle the illegitimate end of the business :