It would be a good deal if you could book the flight in A even though the ticket is only valid for D. The online schedule shows that all three classes are offered from SFO so going strictly by the rules I guess you would have to book in D. However, it would be interesting to turn up at the airport for the SFO-ORD segment and see what cabin they would put you in (if it is 757 operating). If they put you in coach you could argue that the owe rules say that you can be accomodated in first when there is only first and coach offered.
Anyone game to try?