I'd guess that the Championship have two options with there being no Middle 8 fixtures:
1) Increase to 14 teams from 12 with everyone playing each other home and away plus a Summer Bash game giving 27 fixtures, or
2) Stick with 12 teams, play 23 games, then split into two groups of 6 and play a further 5 games to provide 28 games.
League One will either have two teams fewer with 12 teams instead of 14, or they'll have 14 teams like now.
If League One drops to 12 teams, they'd probably have to take option two from above to make their fixtures to 28, but that might overload the system if they want to have a play-off arrangement for teams 2 to 5 for the second promotion spot (assuming it's a 2 up, 2 down).
Three teams going up this season would certainly help the Dons as it opens up the possibility of playing at home in the play-off final rather than away to York or Bradford.