I think the success of something like this would depend a lot on how much OOTP participates. I think folks will get bored pretty quickly if they have to choose their own matchups. Mainly due to there just being so many matchups to choose from. That being said, if OOTP provides daily matchup challenges or every other day etc. I really think this could be a blast.
There could be theme weeks/months, such as World Series month where all the OOTP challenges involve teams that met in the World Series. This could expand to involve matchups of great World Series teams like the 27 Yankees against the 84 Tigers(I know the obvious choice there is the 75 Reds, but hey, I'm a Tiger fan....at least it's the same great managers
).
There could be a home run week/month where all the matchups involve teams that hit a ton of home runs. What about a week where all the matchup involve teams that hit a ton of home runs vs teams that were built around incredible pitching?
My point is, the options are endless, but I really think we will need OOTP to lead the charge in suggesting the challenges.
Here's another thought. This again is based on the idea of OOTP creating weekly or daily challenges. How cool would it be if OOTP were to use the results of the challenges to create OOTO challenge tournaments. For example, let's say a challenge begins using the World Series matchups of the 80's. After everyone is given the time to play each series as both the top dog and the underdog, OOTP could tally the results and use them to determine the matchups for the second round of the tournament. This could go until a best team of the 80's is crowned......which of coursse will be the 84 Tigers.