[Brightcolours]

BC, this is incorrect.
Again, this specific issue only affect some mirrorless cameras, not all of them. Olympus and Fuji cameras do not suffer from a decrease in DR.

Since it affects others it can't be incorrect, can it? Maybe Olympus and Fuji have fast enough read out for 12 receptively 14 bits, but the Sony sensors apparently do not, nor does the GH4 which drops from 12 to 10 bits.

I'm quite surprised your forgot another very important reason: the ability to shoot at a speed way beyond the mechanical shutter like at 1/32000 for instance (thanks Fuji).
It means one can shoot at f1.2 or f1.4 in bright day light. The only other way to do this would be to use a ND filter which is an annoyance, especially when you don't want to mess around when the family is waiting.

You are correct, that it allows Fuji to implement very short exposure times. But the slow read out times make for rolling shutter effects even with very short exposure times.

Again, rolling shutter is rarely an issue, unless one shoots fast action.

Rolling shutter is already an issue when bikers pass the scene, or driving cars.
Two rolling shutter examples from the Olympus E-M5 Mark II:
http://2.bp.blogspot.com/-llpwz1XLig8/VS...050142.JPG
http://2.bp.blogspot.com/-llpwz1XLig8/VS...050142.JPG

Rolling shutter due to electronic shutter with Fuji X-T1:
http://static1.squarespace.com/static/52...ormat=750w
Same subject with mechanical shutter Fuji X-T1:
http://static1.squarespace.com/static/52...ormat=750w

Other issues with electronic shutter:
https://www.dpreview.com/forums/post/56499436
Thee you have a camera shake issue ruining a shot with short exposure time but movement due to the very slow read out.

Then there is the next issue: the inability to sync with flash with (the current) electronic shutters.

Electronic global shutters, which should be the cure, impact low light performance and DR.

Canon, and Fuji together with Panasonic, have filed patents for improved global shutters, so sensor manufacturers are working on solutions.

To be frank, I rather use my 3 stop ND filter on my 55mm f1.2's than having the low read out speed making 1/25th sec motion issues in my 1/8000 sec. exposures...