With the current format, chances are, we'll never get to see a Brady-P-Mann Super Bowl. In the past, there were times when one conference was stronger than the other, which led to blowouts in the SB by teams from the stronger conference.
An integrated playoffs format would make it possible for the best two teams in the league to compete with each others for the Lombardi Trophy regardless of what conference they play in.
Besides, the NFL as a whole is now one fat homogeneous monopoly. Do we need a landmark Supreme Court decision before the league would implant an integrated playoffs system, or what?