[Brightcolours]

The image as seen in an OVF has less qualitative overlap with the final result compared an EVF and the final result is all that matters. Not a hole in a camera.

What matters is how the camera shows the scene. I prefer my camera to show the scene like it is, so I can do my own creative decisions based on what one sees. An EVF shows the scene based on the decisions of the camera manufacturer. 

e.g

Over/Underexposure:

OVF - no feedback

OVF gives the exposure in the metering bar. Over/under exposure is for the photographer to determine.

EVF - full fullback (inc. histogram)

 

DOF-Preview:

OVF - poor feedback

ECF - acceptable feedback

Huh? My OVF gives excellent DOF preview, and the 3D quality an EVF never gives...

White Balance:

EVF - no feedback

OVF - full feedback

My OVF gives me the scene as it is. An EVF shows the scene interpretation of the camera. Not good for a creative person.

Of course, some EVFs are better than others.

 
Other than that the mirror slap induces vibrations that are just not necessary. 

The A7r seems to do just fine with shutter induced vibrations (if one goes by some early user accounts). As do some  MFT cameras with shutter induced vibrations linked with the IBIS. 

 

Now my handheld photography of course never is hindered by mirror slap. If I do things on a tripod, yes, indeed there is never a problem with mirror lock up...

As far as the A7r as a whole is concerned. No, it is not the last word in the game (of course).

It lacks PD-AF and an electronic shutter.

Whether you like the boxy layout - I can live with it but I would prefer something more elegant. But that's just a matter of taste and style.

 

So yes, the A7r will not replace your "average" EOS 5D III ... yet. The A7r II could.

 

That said I question the concept of a tiny full format mirrorless camera. Long tele lenses are just way too big in comparison to the camera.