Aside: I use the 110 on my rb in fact, but it only works for near focus (portrait is ok) unless you do some further modification, and there is no shutter control. All you have to do is pull two little pins to make it mount on the rb though. Very easy.
There is MLU on the rb and rz and, as for silence, well, it's not silent when the mirror slaps, but you can do that well in advance of popping the leaf shutter lens. And the lens shutters themselves are very quiet.
I am thinking that if an rb/rz had a shutter up level, so that you an avoid the kerthunk, those systems would be eerily quiet.