I think that if Ubuntu wants to be succesful on the desktop, it should be targetted at the mainstream markets. All GNU/Linux distributions are way more common in the “early market”. But for these users, other distributions that are more do-it-yourself than Ubuntu are more appealing to them. Ubuntu, as one of the most easy-to-use GNU/Linux distributions is almost destined to please the mainstream market. Ubuntu could already be regarded as a whole product solution. I know it will be hard, but Ubuntu has to try to conquer the area dominated by Windows. Also, I would focus on everyday private users and not on professional users, because they are better off with distributions with a professional support like SUSE and Fedora/Red Hat.
The second law worked out a lot of times for Linux. It is first in almost all new technologies that appeared after the 1990s’ like mobile devices (Android); web servers and super computers. But Ubuntu happens to be in the already dominated desktop-computer market. That means that we’ve to focus on smaller things, that we provide and Windows doesn’t. It’s good that Canonical gave up on Ubuntu Touch and Unity/Mir and now focuses on only providing a very good server and desktop OS, which are realistically the two markets where Ubuntu has a real chance to dominate.
I think that the most important thing is to make Ubuntu better known by the wide majority. We also have to debunk the classic “Linux clichés” like that it’s hard to use and not suited for normal people. Ubuntu isn’t destined to take over a niche, there are way better and more specialized distributions for that. It needs to go far into the mainstream direction. Actually, when you only look at Linux, Ubuntu would then be in a niche. If it becomes no. 1 over there, it would eliminate the issue that Ubuntu is slowly losing the Linux market.
Ubuntu should be targeted at home users and small business users who want an easy-to use, reliable and (very important) beautiful system. Windows these days is very cluttered and constantly updating, so it wouldn’t be hard to catch on over there.