I don't think it really works as a monthly title. It seems to be a concept with a short shelf life, even before you consider the difficulties of balancing a series with two leads who often have drastic status quo changes. I'm not sure Steve Rogers has even been Captain America in half the issues since Brubaker's run (he's been believed dead, replaced by Bucky, stuck in another dimension, aged, turned into a Hydra double agent, and this is before you consider stuff that can happen to Spider-Man.)