Phase One may go mirrorless/EVF, but I will be surprised if they do as it would mean all new glass, or at least an adapter, plus the current LS glass, has quite a bit of weight and a mirrorless body, may not integrate well. The marketplace would be quite small, smaller than traditional Medium format digital is now, and at Phase One's current price point, again I would be surprised to see it.
EVF, that will be Sony, or possibly Fuji as they have the tech in place now and with their pricing model, will reach a vastly larger market.
Phase does have a solution, with the A series, that with a CMOS back, does allow for quite a bit of flexibility. The Alpa TC, is much lighter than a XF body, and you are using the copal shutter, which is basically soundless. Sure it's a very manual solution, but in my case Live View is pretty much always a slower and more manual solution, not to be hand held. Add the iPhone connection and you have a nice package, again costly. But the parts may be cheaper to buy off th used market and put together.
As for the mirror slap, I too had hoped to see a more modern sound to shutter/mirror noise of the XF, but I really don't believe too much changed here from the DF or DF+, I would be surprised if the shutter is anything different and the mirror more than likely the same parts. Phase went for a lot more tech around the firing, i.e vibration reduction mode in combination with the seismograph tech to monitor vibrations. This tech does WORK, and works very well, but as many have noted, it doesn't reduce any of the noise of the shutter/mirror combination.
One last note, is that if you are using a LS lens, and use Live view, then yes, you can reduce the noise quite a bit, and you can do this hand held.
With the IQ100, not sure if this is the case in the 50MP CMOS, when you go to Live view, you have raised the mirror and shutter to be viewed on the back's LCD, thus when you fire the shutter, all you fire is the LS shutter of the lens, and this is VERY quite indeed. I use this solution all the time with the XF and it is a great option.
Paul C