I have not used medium format for wildlife photos so take my opinions with a grain of salt... but for wildlife photos I have been using a DSLR with a frame rate that could be described as 'leisurely' even with a good tailwind and without AF, so I don't see slower frame rates and slower AF as insurmountable problems. The things I'd be concerned about are object field at minimum focus distance, shallow DOF and size/weight for an equivalent angle of view.
