I think for me there are really two competing issues.
First, the idea of working in digital with the same basic restrictions that have always been imposed with black and white film is very attractive to me. With the Monochrom in hand I cannot choose to shoot in color because it is not there. If you really think of it, that is psychologically unique. Obviously my M9 allows me to use color if I want. Even with a film camera I can finish the roll, or rewind early, and insert a roll of color film if I wish. For the first time since color film became commonly available, this is not true.
Of course the opposite side is that you can do the same basic thing with an M3 and a roll of Tri-X, and for a LOT less money. Of course if you digitize the film you will need a scanner, but even with that included it still is far more economical to take the film route, at least from the perspective of the initial purchase price. If you are part of the crowd who believe that digital costs nothing after the initial purchase then at some point the cost of film and developing overtake the cost of the Monochrom. At that point, of course, the Monochrom pays for itself and becomes "free." I am afraid I don't fully subscribe to this idea since there is always some cost associated with any activity, however difficult it may be to accurately assess it. Besides, the initial outlay is usually the big barricade to most people. The thought of eventually amortizing that cost is nothing more than an intellectual exercise.
Of course the film route includes additional costs that aren't always considered, a time and convenience cost, but for most of us our time probably is not worth the additional cost of the Monochrom. Based on quality reviews it may not exactly be an apples to apples comparison either since the Monochrom files may have more potential resolution to use than the same file of a film scan. If you do need that additional resolution than the Monochrom may in fact be a better option for you than film. All of this assumes that the Monochrom is used by an amateur. There are other accounting benefits available to a professional in the conduct of their business that may in fact make the Monochrom a reasonable business expense.
But, for me, the Monochrom, though a very tempting piece of equipment, is not something I am ready for now. Truth be know I may not ever be ready for it. The M9 was a BIG step outside of my financial comfort zone, then and now, and I know that I am not getting all the benefit from that purchase that I could. Though I do not regret that decision right now, there are times when I feel guilty that I am not putting that money to good use by using it all the time. At those points I am sometimes tempted to sell it.
Of course tomorrow I may feel different. Some days it is relatively easy to resist GAS, other days it seems almost overwhelming. But this is the way I feel right now.