Depends on whether you think most of the people paying for NFLST today do so primarily to watch one team's games, or all the games. I think it is mostly the former, and offering a $125 option would cost them revenue.
The way the NFL sells streaming rights matters. Directv pays a flat fee to the NFL because they are getting an exclusive. Without the exclusive, such a flat fee deal makes little sense. All other sports rights are sold per viewer, and the NFL may have no choice but to offer rights the same way. Then it comes down to whether the NFL simply charges per viewer, or distinguishes between per team and all teams viewers. If they don't, there isn't going to be much difference in the per team / all teams pricing since what they pay the NFL won't change either way. If they do, then the NFL will effectively set the pricing (i.e. 50%/100% or whatever) based on what they charge for the rights.