The mirror seems more and more like a relic from the analog period.
The problem (in my eyes): the viewfinder. I like rangefinder cameras - owned a Leica M3 for quite a time and loved it and still have two Fuji 6x9cm RF cameras which are simply GREAT!
The only advanage i see in the mirrorless constructions: you have more choice on lenses. You can use extremely fine
Leica-M lenses, Zeiss RF lenses or others of very high quality . . from which some are much better than usual DSLR lenses -
but also come for a price and provide no automatics of course. All compensations must be done manually.
But that´s how real photography is btw. . .
I can´t see any other advantage. Ok - weight and noise maybe . . .
I never would like to miss an optical viewfinder with a good screen. Those electrical viewfinders in the mirrorless cameras -
i didn´t see a real good one. I know real good electronic viewfinders from RED´s and Arri´s top cameras - but their viewfinders
cost more than the mirrorless camera WITH the lens . .
Which makes sense in my eyes is a viewerless body for UltraWide lenses with an attached optical viewfinder on top.
With ultrawides you don´t need to focus.
BUT: non-retrofocus UlraWideAngles with back-lenses very close to the sensor most likely produce heavy fringing because of
strongly diagonal rays coming from the lens so close to the sensor.
I realized that very intensely when i used a Hasselblad SWC (Zeiss Biogon 38mm, non-retro) and a Phase One digital back:
excellent lens (definitely one of the world´s best UltraWides), excellent back (no question), together about 20000.-€.
The results were far away from what i expected.
Because of the fringing is non-linear it´s hard to compensate without losses.
So: whether mirrorless cameras will or will not take over the universe - who cares?
When you are good - you can use *any* device for making good pictures.