Get out a few items from your kitchen drawer and play along with me here.
You'll need the following:
A yellow drawing pad and a pencil.
A small plastic or wooden school ruler.
A small plastic drawing triangle.
A Hasselblad 500 C/M camera with 80mm Zeiss Planar lens.
Your current mirror-less or DSLR camera.
Seven envelopes and seven stamps.
First, put your digital camera to your eye and take a picture while looking though the viewfinder - lens on auto-focus, aperture on f:11, and shutter speed on auto. Review it - looks good, eh?
Now hold the camera at arm's length and sight through the LCD for the same shot. Look a bit shaky on the screen when you play it back? That's you shaking. For another $ 3600 you can have the next model camera that will remove that shake.
Third experiment - hold the camera close to your body at waist height and shoot the shot. Looks a bit less shaky on playback, eh? Just as good as the eye-level one? But you had to guess the framing? No tilt screen?
Now pick up the 'Blad and open the waist-level finder. Focus the 80mm lens and take a shot. When the lab returns your transparency in three days you can see whether you held it steady at waist level - and likely you did - and you could see to sight it accurately.
Now for the yellow pad and the pencil. Draw a camera body on it the same size as the Hasselblad and put a drawing of the LCD screen from your current camera on the top - in the waist level finder position. Draw a folding hood that covers it when not needed and shields it when it's open. The left side of the camera can be as plain as the Hasselblad or you can put some doors on it covering mic or flash ports.
The menu and function buttons or D-pad can be on the right side - the shutter release on the left or right like a Hasselblad or Rollei. You can put an ISO dial where you like.
As you'll use the same lenses as you do now, they can run on AF or MF. Plenty of space in that body to place the sensor of choice. plus SD card and adequate battery. You have a waist-level mirror-less camera.
Copy this drawing seven times and post one each to Nikon, Fujifilm, Sony, Panasonic, Olympus, Pentax, and Canon. Write their addresses nicely - you are making a polite request.