It's not hard to imagine how the playoffs would function with an expansion to seven playoff teams in each conference: the top seed would get a bye and the next six in each conference would play in the opening weekend. Once those games were done, they would be down to four teams in each conference, and things would proceed as they already do.
The additional two playoff games on the opening weekend (six total vs. four currently) could either be jammed into Saturday and Sunday or spread over three to four days (Friday-Monday).
It's hard to muster a whole lot of outrage about it since, as Kevin Seifert notes on the link above, the team that would have been the No. 7 seed in each conference in each of the last 11 years would have, more often than not, been at least 9-7 and never worse than 8-8.
That said, it does seem to cheapen the regular season a little. While it does give the No. 1 overall seed an advantage over the rest of the teams (currently the top two seeds get byes in each conference), you are letting in one more team that could potentially make a run to the title almost as easily as teams with records much better than them. If you were the 12-4 Patriots this year, wouldn't you be annoyed that your only edge over the 8-8 Steelers in a first-round matchup was home field advantage?
As such, we would propose going a step further: Why not make it an even eight teams in each conference that make the playoffs? Then give the top four teams in each conference -- we can argue over whether these should be the four division winners or simply the four teams with the best records -- a first-round bye and make the four lowest-seeded teams battle it out in an extra weekend. In the next round, the top two teams in each conference get ANOTHER bye while the opening round winners face the No. 3 and No. 4 seeds -- the equivalent of what is now the wild card weekend. Then proceed with the current format in the rest of the rounds. It would require an extra week, which is easy: finally get rid of the stupid Pro Bowl, which is now jammed between the conference title games and Super Bowl, and just have one week between the conference title games and Super Bowl to avoid some of the relentless hype.
The benefit we see is this: if you are one of the four lowest seeded teams (5-8 in each conference, it would mean you had to win FOUR games just to reach the Super Bowl. If you were the No. 3 or 4 seed, it would mean you had to win THREE games to reach the Super Bowl. If you were one of the top two seeds, it would mean you had to win TWO games to reach the Super Bowl. Basically it would make it harder for teams that squeak into the playoffs to make a Super Bowl run and give extra reward to teams that prove it over a 16-game schedule.
Adding two more playoff teams in each conference would give the NFL the extra revenue it craves from more games, keep even more teams in the playoff hunt in December and make the system more fair all around.