I am testing the Windows 10 Technical Preview for Enterprise, build 9879. I installed Start8 v1.47 and am pleased to report that it works very well with Windows 10 thus far.
Windows 10 is still in development so there's no way to know what the final version of the Windows 10 Start menu will look like. In build 9879 it's a combination of the 'old' Start menu and the Start screen and looks like the dog's dinner, hence my interest in Start8.
Does Stardock plan to develop a version of Start8 for Windows 10?