You can add app shortcuts to the desktop which launch in freeform multi-windows, a feature which first launched with Android 7.0 Nougat. You can also set a custom wallpaper for the desktop. The status bar and navigation bar seem unchanged, but you have a lot more room to work with now.
It’s possible to enable this desktop mode by going to Developer Options on a Google Pixel, Pixel 2, or Pixel 3running the beta and enabling the “force desktop mode” Developer Option, then launching the activity in the Pixel Launcher using the “GMS” command from above. You’ll need to change your Pixel’s DPI before casting or connecting your phone’s screen to any external displays, though.
This certainly looks interesting and is something I'm going to keep an eye on as we hear about more practical ways this may be used. Looks like Android Q is certainly going to be bringing quite a few new interesting features. I'm also really keen on the full dark mode.