That's display gravy. Evidently it's cool to look at, but it must be CPU/GPU intensive, would it? Would it be possible to not compute when the user translates or rotates the view? Then it would not impact display performance too much.
Is it useless? Quite!
But pro CAD software already do it: NX as is shown in the screen capture, and SolidWorks as well. Possibly the late versions of Solid Edge. And it's real-time rendering too.
Google images made on SolidWorks, it seems many people hardly go to the trouble of doing real renders when a simple screen capture looks that good. (I'm not saying it looks as good as renders, but that the image quality is sufficient for most people)
But something as good looking may require some special hardware and drivers.
The image below is a screenshot of a data set from NVIDIA shown in SolidWorks with RealView graphics on. RealView graphics utilize the GPU to render the semi-realistic graphics on the SolidWorks screen. The other window is the PhotoView 360 Preview window. PhotoView 360 is 100% CPU-based rendering and doesn’t task the GPU, so for PV360 rendering your benefits come along with more multi-threaded CPU cores. The SolidWorks models are all CPU as well. The GPU does little for processing the model, so more GPU’s won’t gain you any added performance. (link
It's a matter of perception. Some new users coming to FreeCAD may find the utilitarian
way it displays parts bland and think it's primitive. Their opinion of FreeCAD may very well be influenced by such an insignificant detail.
So I think it would still be fun to have it, if it's not too much trouble to implement.
Of course that would have to be an option that you can disable in the display preferences.
Even if this seems superficial (and it is), it would help make FreeCAD look like a "modern" CAD software.