This is less about realignment and more about management of college football. When the SEC expanded the Pac 12 was the first to say, "we should pause this expansion of the playoff" and the Big Ten, through Ohio State, kept the conversation going. The money growth, going forward, is in the playoffs with one network claiming, "why bid on the regular season if it doesn't include any post season games?". The SEC's move to grab TX/OU was to try and grab as many spots in the 12 as possible, with ESPN controlling all the properties. Two things occur by waiting:
1) You force the SEC to have less teams in the playoffs, even if TX/OU move early and
2) By waiting 5 years you allow other entities (network or streaming) to bid on the post season instead of allowing ESPN to keep it longer.
This "alliance" if it comes out, would be about voting control to ensure the end game stays even, and devising a system to balance the scales further, like the auto champs, etc. Much of CFB is now looking at ESPN wearily.
I expected this from the Pac/Big Ten, but it was a bit surprising to see the ACC involved. They must be equally pissed with the SEC's moves. One of the best moves for the Pac/Big Ten right now is carve up the Big 12 until both are at 16, play 9 conference games, then play a home and home scheduling alliance to get to 11. This would allow both conferences to take more inventory, of higher quality games, to market to sell, increasing the value of the deal. Hell, some could be designed to be made for TV, launching the season with the top four from each conference playing each other in like DC, Chicago, Denver/Phoenix, LA like the SEC does with the CFA.
Having the Pac/Big Ten matched up with 32 teams controls half of the current P5, adding the ACC, with ND, controls 74% of the votes to counter the SEC/ESPN block.