I would keep the current playoff committee and still have them rank teams weekly. IMO 8 teams would be broken down something along the lines of:
Each of the 5 power conferences gets an automatic bid. The conference champion does not get the automatic bid but rather the highest ranked team from the conference as determined by the CFB playoff committee. This would eliminate 3 and 4 loss teams that happen to win their conference championships in a down league year.
The highest ranked team from the Group of 5 if ranked in the top 12 by the playoff committee.
Two At Large Teams (Three if the Group of 5 team is outside the playoff committee's top 12).