A couple thoughts:

- When you get rid of the mirror, that means you're also getting rid of the mirror needing to flap up and down. That increases camera stability for longer exposures. (It's also one of the benefits touted by expensive rangefinder cameras from Leica and others.)

- I find I can stabilize my Panasonic LX5 (screen-only, no viewfinder) just fine with my elbows at my side, and looking down at the screen.

- Cameras with a flip-out-and-rotate screen are even better in this regard because you can now truly shoot from the hip, which is even more stable than in front of your face. This is the default shooting posture for somebody with many older medium-format cameras.

- For something like the LX5, that lacks a viewfinder, you can purchase a variety of third-party optical viewfinders that click into the flash hotshoe. Panasonic also offers an electronic viewfinder that clicks in, specific to the camera.

- Battery life on my Nikon D700 is superlative (thousands of pictures on a charge). Battery life on my Panasonic LX5 is still remarkably good (400+ pictures on one charge). So long as I've got the flash off, the screen doesn't seem to be an impossible sink for the battery.