A few bits on some of the scenarios people have mentioned that I've picked up.
I had it explained to me by Paul Duffen, so make of that what you will and this is on the assumption they haven't changed, that the PL and EFL have an agreement that the PL will relinquish three 'golden shares' to the FL every season. I don't think its anything to do with the PL how those shares are distributed (for example, the PL had no say on the extension of the play-offs as of next season). So my understanding is that three teams will come down from the PL and three teams will come up from the FL no matter what.
If Southampton are fined, the money will be shared between the clubs of the Football League (as is the case with all fines to clubs). Should the date of the play-off final be changed, the fans groups are already prepping to pressure the Football League into that money going towards recompensing Hull City fans. That may be entirely futile, and I've no idea how workable it is, but it's got to be worth a try.
Another factor is that there is an agreement, apparently, that the loser of the play-off final gets to keep the gate receipts generated. This would be yet another potential headache within this whole farrago. As Southampton could recoup a large amount of their fine by losing a final they should have been banned from.