this is a fantastic question. I would go behind just one promo that I would like to see, though. EA should have a consulting board of amateur Madden players, who would obviously be willing to donate their time (but would be helping EA make a lot more money by delivering actually good content), and whose role would be to come up with the ideas for at least some of the promos during the year.
If I had to name a promo, though, it would be a fan art promo, where amateur or pro artists contribute fan art or player artwork, and it can either be incorporated into the PUP or the fan favorites get new items during the promo and after the voting. You could have the artwork unlock after solos, or you could have voting done by completing certain solos. To expand this, I would also include uniforms and stadiums; concept art could be done by the artists submitting and then a select few could be added to the game by popular vote or whatever. Even better would be if you could unlock one customizable uniform item through a string of solos or as a level reward (Think of the team builder tool for NCAA Football 14, where you could upload logo images on a web interface and customize colors and other elements on the uniform).
