Retina resolution in macOS guest in Parallels Desktop for Mac
Yes, now in Parallels Desktop for Mac version 12. This new version released 2016-08 is the first to support Retina resolution within a macOS VM. 

Per this page, Parallels Desktop 12 for Mac: Updates Summary…


  Retina resolution support for OS X virtual machines


Previous versions of Parallels, as well as the competitors VMware Fusion and Oracle VirtualBox, provided some support for high-resolution resolutions in VMs of other OSes such as Windows &amp; Linux, but none did so for macOS-as-guest VMs.

Here are screen shots of the three new settings. The first was the only behavior in the previous versions without Retina support.



This next shot shows the new Retina support. Zoom into these images to see the difference at the pixel-level. You will see the icons in the next image are much more detailed than seen above, and the edges of fonts and lines are much more fine than seen above.



The last shot is if you want to use every physical pixel as a logical pixel in the display, rather than take advantage of Retina smoothing. So you get the most usable visual space but at the price of making everything tiny and harder-to-see. Notice how the Finder window becomes zoomed-out, showing much more content but shrunken.



Bug

I have encountered a bug where after adjusting for Retina, when using the VM on an external monitor (not Retina) the resulting image is shrunken, not re-scaled for non-Retina. So text and graphics are squished with too few pixels to represent their true detail.

See the following screen shot of part of screen when running Parallels 12.0.1 on an external monitor. The monitor is a plain full-HD Acer brand monitor, non-Retina. Notice how the Apple logo on the menu bar is smaller than the Apple logo on the host Mac, and the menu labels too are shrunken.

While on the non-Retina screen, the scaling options disappear. So I cannot find a way to return to conventional scaling within the VM.



Workaround is to open the laptop, move VM back to Retina screen, access the Configure panel, choose the third Retina option "Scaled", move VM window back to conventional external monitor. You may then close the laptop.