I think that the target audience for such a calendar would be women/mothers/hospitals/doctors offices etc. Anyone that would buy it for sexual gratification I think would be sorely disappointed, especially considering that the photos would be carefully selected. I think it would be nice to focus on how discreetly, comfortably and conveniently one could breastfeed in public and at home. I don't think that there is any need to 'promote' bottlefeeding as such as there is enough of it going on by people who can not or choose not to breastfeed as well as people who wean from breast to bottle. I would hope that focusing on breastfeeding would be understood by all those bottlefeeding groups on health grounds, and of course promoting Breast is Best is a generalisation not a prescription for everyone and every situation.
MN could do an annual calendar. One year it might be breastfeeding, the next special needs, the next relationships etc etc. A good promotion of MN, a bit of a money spinner etc. Besides the photos the calendar should be designed so that people can fill in activities and appointments under the dates - we know how busy a mums life can be. Rambling now, so will stop.