It may be academic now (and one hopes it always will be) but

[Neil D]

There's an interesting suggestion in the i today that the play-off procedure should be amended so that 5th plays 6th with the winner playing 4th for the right to contest the final with the 3rd placed team at Wembley.  The argument is that there should be a greater reward for finishing third than merely playing the second leg at home.  It would have been a very bitter pill to swallow if we had lost out to a team which finished 13 points behind us.  In Italy for promotion from Serie B, the third-placed team, if it finishes nine or more points ahead of the team in fourth, is automatically promoted.  I think some tinkering is overdue.  It's worth remembering that the play-off system was only meant to be a one-off with the first three automatically promoted.

[Stephen1984]

In Scotland to win promotion to the Premier league, the 4th and 3rd In the Championship play home and away. The winner then plays the 2nd place team in the championship home and away then the winner of that plays the 2nd bottom finishing team in the Premier league again home and away. The winner of the final tie gets promoted (Livingston yesterday beating Partick Thistle over 2 legs.)

[barters]

The conference leagues have changed their play off system this year.   1 team promoted and next 6 go in the play off's - 4 v 7 with the winner visiting 2. 5 v 6 with the winner visiting 3 with the semi final winners playing the final.      Seemed to work really well with one off matches, clearly seeded to ensure the highest placed teams had the best chances.

[Southdowns White]

Just scrap the whole play off system, If you finish in third you should be promoted and if you finish third from bottom you should be relegated. The whole thing is a money making exercise and nothing more, Us, the supporters who go week in week out are the real losers here paying well over the odds for a ticket at Wembley and the winners TV and people who don't go throughout the season. Why should the teams who finish  4th 5th and 6th have a second chance to beat the team that have accumulated more points over the season? I am very excited by the prospect of having a day out at Wembley on Saturday but would have prefered to have either gained or lost promotion by the results in the league.

[Twig]

Just scrap the whole play off system, If you finish in third you should be promoted and if you finish third from bottom you should be relegated. The whole thing is a money making exercise and nothing more, Us, the supporters who go week in week out are the real losers here paying well over the odds for a ticket at Wembley and the winners TV and people who don't go throughout the season. Why should the teams who finish  4th 5th and 6th have a second chance to beat the team that have accumulated more points over the season? I am very excited by the prospect of having a day out at Wembley on Saturday but would have prefered to have either gained or lost promotion by the results in the league.

I must admit that I have always held a similar view.  On the, generally accepted, basis that the table doesn't lie then the third place team deserves promotion.  It's never goung to happen though because playoffs are such huge revenue generators.  Given that, the System proposed in the OP has some merit.