I think this would be extremely useful in increasing Linux desktop adoption. There's an enormous number of Windows users who hate Microsoft's changes to the Windows GUI and wish they could still run XP or 7. There's also a need to make sure it is stable enough that users never have to resort to the command line and that it runs "non-free" software out of the box, especially software originally developed for Windows. The latter, of course, is a necessary compromise to get people who aren't FOSS purists to use the operating system. I think the focus should be on Windows rather than Mac because Mac users generally like Mac.

Linux adoption, in my view, is held back by the existing community's lack of desire to deliver what the average user wants. Things are obviously better on that front than they used to be but Ubuntu is still quite bad at doing what non-technical users want from a computer. Most Linux users seem perfectly fine with that.