Thanks for all the input. We have a Sony NEX-6, A5000, Canon 5 M III and various other compacts. The problem is more that we have to use a lightweight platform due to the flight weight requirements, especially in Germany.
Preliminary tests with stereo Mobius were good for what we do (river mapping and modelling) so we are going ahead with the Mobius multi cam design. Right now, including 5 cameras and integrated USB hub we are looking at a total mass of 1.2 kg, which is pretty good.