I have to disagree on this. The Linux Desktop (once installed) is ready for "normal" users and has been so for years; and not just theoretically, I personally have installed Linux on several PCs and the only maintenance I have to do is reinstalling it when the person buys a new PC.
I think this is true for 80% of the users out there, who basically use their PC as a "click here to open browser" device (and viewing some photos etc.). However, ChromeOS does that even better than Linux admitably.
The problem is with the 20% Windows power-users / gamers, for whom Linux is not a suitable replacement as it works differently and is easy to break if you have only dangerous half-knowledge. While these people certainly would be capable of learning Linux, I don't really see that happening as they often show open hostility to any system that is doing things differently than what they are used to... and in a sense that is understandable as it is a sunk cost fallacy of having spend considerable time to learn how Windows operates.
I highly doubt that Linux will be ever able to cater to those 20%, even if there are certainly some areas that could be improved. But those users will just find some other issue to nitpick about...