Basically this is the "same" idea as force Nautilus to open in new tab instead in new window, just for Kubuntu.
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Dolphin has split view option which is even better than tabs as you can move your files much easier from folder to folder.
So when I have my Dolphin open and I want to open another Dolphin the first Dolphin should just split view to a folder that I opened with the second one.
If there is already a split view opened in Dolphin it should add a new tab instead, then split view, then tab again...

I hope you get the picture.
And if I close split view in both tabs they should be merged in one split view.

on large screens there is a plenty of space for main area in dolphin

it can be split into two smaller areas

what if each one of them could be splitted once again?

for ex i would have one area on left with my home dir and on right - two more, this would be very usefull when you have to move files between more than two directories

I absolutely adore the Dplhin view where you have folders and folder contents (files) in one tree.

But as it is made today, it uses a lot of vertical space in the window, while no horizontal space is used, because the files as well as the directories are listed only vertical below one another, like in a classical list view.

However, today we have 16:10 displays that provide 60% more space in the horizontal direction than in the vertical.

So what you get with this beautiful view is a lot of directories and files on the left side of the window, a big empty window and some file/directory information (like byte-size, owners, read/write-rights) on the left end of the window. That space should be used more efficiently.