You're not adding an extra loss. You're losing a guaranteed in-conference loss and gaining a possible out-of-conference loss. On the whole, your conference will have fewer losses.
Also fewer wins. And playing the Big 12's second best team is usually an easier task than playing the Pac 12's best team.
I think the game will serve as an elimination game and I don't think it makes sense to add an extra, tougher hurdle for the Big 12 to pass in order to get to the playoff. Plus, without a championship game, the Big 12 returns to the problem of crowning a "champion" in a ten team round robin. The whole thing seems like an enormo pain in the ass with no real benefit.
Fewer wins is okay in terms of playoff chances. It's just the late season loss that you want to avoid.
I don't think we have enough information to guess whether this would help or hurt the B12's chances of getting a team into the playoffs. The number of scenarios that could happen is so huge.
I don't like any of the B12's options for determining conference champion, so I don't feel like we'd be losing anything there.