a modern mod would be possible due to the workings of modern warfare and the stability of todays world, it would have to be set in either a small ficticous central african state during a civil war and even then plausibility wouild be streechted to the limits, the 1930s would be a good setting if you wanted modern, as for a couple years tthere almost all the nations in europe were on the brink of civil war, and it was really on the common threat of the germans which prevented the collapse, the Spanish Civil War would be a good setting for the M&B style of game, but since then even the revolutions and anarchist have been organised. a near-future setting could work, but who knows. The distant future would be perfect, because as we know from science fiction, the future is either going to be the middle-ages but with technology and space travel or the 1870s midwest. still, no worries, probably anything is possible if you put enough work into it.