I think things are shaping up and will take care of themselves. Like others have said, the only thing that matters is being in the top 4 at the end. My take:
Clemson - If they win out, they are in. No questions asked. If they don't beat NC, it could be tough because I think the committee will hesitate to take anyone who does not win their conference. Clemson is the only one of the top 4 that can survive a loss.
Alabama - Win out and we are in. Period. Two losses = no way of making it even if they beat Florida to win SEC. Auburn would love nothing more than to spoil a championship run for us.
Ohio State - Win out and they are in. I agree that they have not played anyone of substance yet, but they have not lost a game either. To win out would require the Buckeyes to beat: Michigan State @ home, Michigan @ the Big House, and an undefeated Iowa team for the Big 10 Championship. Their tests are just coming later in the season. No other team has the chance to close out like the Buckeyes. That being said, I think the committee drops the Buckeyes if they lose a game because of their weak play up to this point.
Notre Dame - Win out and they are in. Their only loss would be by 2 points on the road at the potential #1 seed Clemson. No way they don't make it if they win out, but Stanford will be a tough game. BC always plays ND tough as well & it is a neutral site game. Notre Dame is playing really good football right now and will be tough to beat. They actually benefit this year by not having to play in a conference championship game. They have a quality resume, but 2 losses = no title shot.
Iowa winning the Big 10 Championship by beating Ohio State really creates havok. How do you leave the undefeated Big 10 Champion out of a 4 team playoff when the Pac 12 won't be represented either? I think Iowa has to make it if they win out, and they will eliminate Ohio St by doing that.
Oklahoma makes a case if they win out, but that Texas loss is bad. They definitely need some help to get in, but that help could happen.
The only one of the top 4 right now that could survive a loss is Clemson in the ACC Championship game, but I still have a hard time seeing the committee taking a non-conference winner. I would take a 1 loss conference champion over a 1 loss Clemson every day. There are too many choices of conference winners. If Bama or Notre Dame lose again, they are out.
The final four at the end of the year could very end up being Florida, Iowa, Oklahoma, & whatever team has 1 loss coming from a conference championship (OH St or Clemson).
I think it will end up being: Clemson, Bama, Ohio State, and Notre Dame. The committee will probably take the "Rematch Route" and pair Alabama with Ohio State and Clemson with Notre Dame. A lot of people will want to see these games, and the winners get to play for the title. This is why I love college football.