I don't agree that there will be a ton of Packers fans there. It's tough to put together a plan to get to a playoff game in less than a week. People look at a regular season game where Packers fans or 49ers fans or Steeler fans have a ton of time to get tickets and make travel plans and end up with a ton of people in the crowd. The playoffs are a different thing altogether.
I went back and looked at my pictures from when we played the 49ers two years ago. There were definitely some 9er fans there, but not more than 10-15%, and that's another fan base that typically travels well.
I've been to every playoff game at AT&T stadium and they are all a great environment. That 49er game went south quickly, so that was probably the worst crowd, but I would blame the team more than the crowd for that one. Not much to cheer for.
Went to the Cowboys/Eagles game earlier this year and the crowd was fantastic for that.
What a lot of fans as well as the media tend to miss or ignore is the proximity of non-Cowboys fans to AT&T stadium.
Some of the old school teams like the Steelers, Packers, etc. have a lot of fans all over the country, so many of them do not have to travel far to go to games at AT&T stadium.
Other teams like the 49ers have a large number of fans in Austin because a lot of northern California companies moved their operations to the Austin area (aka: Silicon Hills) over the last 15-20 years.
Of course some diehard fans of Cowboys opponents are going to travel to AT&T stadium if their team is playing there, especially if their team does not make the playoffs very often, because it is one of the nicer stadiums and it is not too far from DFW airport, which is a hub airport.
In any case, I think most Cowboys fans assume the stadium crowd is quiet because you do not hear a loud crowd when watching games on TV compared to other stadiums, but that's because the recording equipment is farther away and/or more sound isolated than it is in some of the older stadiums.
It seems like every time someone reports from a Cowboys game they went to at AT&T stadium they mention how loud the crowd was during the game.