How will a potential 28" 4k display work?

Hey,

I'm just trying to wrap my mind around something I don't fully understand, after just ordering my nMP!

Ideally I would love a 27-28" display with the exact same screen estate as my current 27" imac, but at retina resolution and videos/images being shown at their respective actual resolution - just like on the rmbp.
BUT- from what I read, to achieve this, the screen would have to have some sort of 5k resolution, in order to scale down x2 to get to the 2560x1440 resolution of current 27" displays right?

Since such panels are not gonna be available for a while nor is it clear how our mac pro would handle 5k - if the displays native resolution would be the same 4k 3840 × 2160 as for example the Dell 24" - would we then get "just" Full HD 1920x1080 resolution if we didn't want ridiculously small fonts but the retina look of the rmbp and use hidpi mode?

I've never owned a rmbp so I dont know how it precisely works. But obviously you can chose between different scaled hidpi modes, while the ones that give you larger workspace have a lower pixel density but still look good?

How good to they look actually? Is it still comparable to a "regular" screen at that particular native resolution? I guess if so, this would be the way for apple to implement 4k on upcoming displays for the nmp?

Sorry for the weird chain of thoughts. But can please someone clarify this for me

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Ok so I did some more reading of how the settings on the rmbp offer you those 5 different types of screen usage from retina over large text to more space.

So how does 1080p on a rmbp look like? Is it comparable or even better than a native 1080 display?

Wouldnt it just be a software update to OSX to do the same for the nmp so we could then display, let's say 2560x1440 on any 4k display?
That would seem like the perfect solution for me?

Ok I sent feedback to apple to please add some interpolated resolutions for the nMP and 4k Displays just like on the rmbp. Maybe you should do the same
http://www.apple.com/feedback/mac-pro.html

Hm, of course I read the anand review over and over again before I finally hit the purchase button.

By now I also found this thread:
https://forums.macrumors.com/showthread.php?p=18588768#post18588768

Some folks seem to have gotten it to work in the past with Switch ResX somehow on lower Res displays.
But still I'm a bit confused. So because Apple didn't yet approved for any 2560x1440hidpi mode in any device, but only the 1080 move for the rmbp, the switchresX workaround just won't work?

If that's the case It can only hint to one thing, and that's apple waiting to enable this until they push out their own 4k Display, to then present this as a feature.
I guess we'll just have to wait until that 28" dell comes out and see if apple gives a software update to osx in time, otherwise i'll just get a regular TB display and sell it when a 4k version comes out.