In case anyone was curious what it looks like 
I diddn’t realise you could exclude applications from the high DPI mode… nice …
now I just need 2x 4k monitors and a slient Graphics card to run them…
I guess the video shows Cubase without highDPI display settings activated. I didn’t like it, as icons and text are just too small and a pain to read on a 24-28 inch monitor.
I’m still trying to find out an answer to this: Does Cubase 8 Pro really look better and convenient on a 4K display, i.e. does it take advantage of the additional pixel density for better text/image clarity, without making text and icons a pain to read?
Thanks.
Philips makes a 40" UHD monitor, and it goes for around 850 euros :
You get the same PPI as on 27" 1440p with a 40" 2160p.
55" UHD TVs should be about as comfortable as 4x 27" 1080p monitors, too (although TVs tend to have higher input lags).
I have a 28" 4k and a 24" 1920x1200 monitor, cubase actually looks worse on the 4k monitor, everything is blurry. Hopefully 8.5 will fix this.
See this thread