I've just done a rebuild of my machine with Windows 10 build 10074 and Visual Studio 2015 RC. For my Windows development rig at home I run a multi-monitor setup comprising my Surface Pro 3 in its dock, and two external 1920x1080 resolution screens. Here you can see a screenshot with all screens represented and the tail end of the Visual Studio installation completing.

Multi-Monitor Setup

As you can see I have the two lower resolution (but larger) external screens sitting above the higher resolution (but smaller) Surface screen. I noticed an interesting thing when I dragged the Window from the Surface up onto the top right screen.

The screenshot below shows the Visual Studio installation window partially dragged with just the top showing on the top right screen.

Partial Drag 1

As I dragged the window further it resized itself to maintain the same window size relative to the screen size.

Partial Drag 2

There seems to be less scaling issues in this build, but the fonts are still fuzzy. When I get a chance I'm going to experiment with the settings but I can tell that they are trying to solve what is actually a pretty challenging problem.