I'm not sure this really confirms that Doc wants his son on the Celtics.
If anything, it seems he's just taking a chance to talk up his son, and provide plausible deniability if the C's do pass on him.
Personally, I don't think the C's will ever have a chance to draft him. I just don't see Rivers lasting past pick 15, he's too good. And honestly, I think Doc would rather that happen anyways. But, if he does, the C's will have to pick him. If he is still available, he will be the best player available almost assuredly.