Loren's suggestion really only holds up if the parable is authentic to Jesus. While the Jesus Seminar may have thought it likely, I don't. An obvious caveat in this regard is its length: It is difficult to remember, and thus harder to attribute to early tradition.
Loren notes, regarding his perception of misplaced emphasis on repentence:
"[R]epentance" is never mentioned in the parable; the younger son comes home because he's hungry.
I think this argument is misplaced. Repentence is not mentioned in the parable of the lost sheep, or the parable of the lost coin either, but the meaning in both is, I think, quite clear. The analogue is between absent//sin and return//repentence in both of the preceding parables, and, I'd suggest, in the third. There are other analogues to further this: celebration occurs both in the parable of the lost sheep (15.6) and in the Lost Coin (15.9). This points, IMO, to the meaning of the celebration in The Prodigal Son, a meaning made explicit in 15.7 and 15.10. Likewise the rejection of the ostensibly greater--the 99 sheep, the 9 coins, the son who stayed home--is a theme found in all three parables.
It seems to me that this parallelism requires a remarkable coincidence, or a single mind working toward a single goal. It is not enough, I think, to suggest that that mind was Luke, working with existing material--the weave is too thorough for that to hold.
Additional weight can be found in the preceding of all three of these parables with an implied or explicit explanation (the Lost Sheep is implied by the grumbling of the Pharisees, the next two are explicit--15.7, 10). That Luke wishes us to read it that way is apparent, though without viewing it as Lukan redaction his wish might be irrelevant. However, there is a curious parallel in theme in the Lukan narrative and Lukan intent and the Matthean parable of the Two Sons (21.28-32). Employing (as I do) Mark without Q, it seems there is a better than passing chance that Luke has made clear what Matthew left oblique.
That said, if the parable is not viewed as a Lukan creation, then I think Loren has offered a convincing exegesis of it. But, in my view, that is a big "if." Nonetheless, thanks to Loren for sharing an interesting and thought-provoking take on the Prodigal Son.