Win 10 64 bits
Worked: Previous builds
Exact steps for others to reproduce the error
This is probably related to the new user preferences autosaving feature?
So to start fresh you need to delete the userpref.blend file inside the folder %appdata%\Blender Foundation\Blender\2.80\config
Now launch blender and go to Edit -> Preferences -> Themes and choose let's say, Blender Light, and then close Blender. (Sometimes It crashes in this step as well)
Now repeat this process again, go to Edit -> Preferences -> Themes -> Blender Light. (Blender will crash when choosing the theme)
There are some rare cases where it doesn't crash, but most of the time it does.