Sure it does. Why would a conference put it's best team through another game with the potential for an upset when one conference isn't going to bother? With a bigger pool of playoff teams, the Big 12 could tip the scales. Especially if they end up with two one loss teams, again and the lesser is called Texas or Oklahoma.
You are thinking in terms of the current system, not the hypothetical system we are discussing. In the 5 + 3 format, each P5 conference would have an
automatic bid to the playoffs. They get that bid no matter what. Nobody can take it from them. Therefore, it doesn't matter if a conference's best team has to play another game with the potential for an upset. For example, let's say Clemson was 12-0, and was upset by 9-3 Virginia Tech. Well, then Virginia Tech would get the
automatic bid to the playoffs. The ACC would not lose its playoffs spot. The ACC would be guaranteed that its champion made the playoffs. Therefore, it doesn't matter if the Big 12 had no championship game, because the Big 12 could not take the ACC's spot.
Now, if you want to talk about the 3 at large bids, it wouldn't matter then either. Let's continue with my hypothetical example. Now, Virginia Tech is in automatically, and you have 12-1 Clemson in line for an at large bid. Now remember, the other P5 champs get in automatically as well, so they aren't competing for those at large bids. Let's just say Ohio St, Washington, Oklahoma, and Alabama were the conference champs. Well, Clemson at 12-1 would not be competing with those teams for a playoff spot. Those teams would get the automatic bids. Clemson would be competing with other 2nd place teams (say, Baylor, Utah, Tennessee, Michigan) for the 3 at large bids. Again, the Big 12 not having a title game doesn't affect this.
However, for the record, the Big 12 is going to have a title game starting in 2017.