A 200mm f/5.6 macro could make sense, within some limits. Other macro lenses tend to be f/2.8 to allow AF to work at closer focus distances, since at 1:1 macro the effective aperture of a f/2.8 lens is f/5.6, the nominal limit of phase AF. If you sacrifice close focus AF, then making the lens f/5.6 would make it significantly cheaper and lighter. Bear in mind the depth of field in macro is already very thin, most macro shots are stopped down, so I don't think the slow aperture will be an issue in this application. Overall I think it would be very niche though. Near macro it would be MF only, which is ok for most macro uses, but would you want to use a 200mm f/5.6 AF at further distances? Might as well make it MF only, and offer more than 1x magnification, like a long version of the MP-E65.