My mail is that the 4/7 rule has pretty much run its course because the 6th and 7th aircraft probably won't ever arrive, and we already have the numbers to comply with the 4/7 rule for 5 aircraft. Therefore the majority of command slots in the future should come from SFO's.
That said, if there are no more aircraft coming, the only command slots will come from attrition. There is a reasonable amount of older guys who joined from Singair and CX who will be moving on in the next year or two, so there is definitely some room for movement for SFO's, but not a lot.
Once the 4/7 agreement has been met, I doubt that there will be another 73/ejet captain offered a slot ahead of SFO's. But I could be wrong.