Unless they can find a way to make "every program ever written" to be touch-friendly, this too shall fail. BlackBerry must have some kind of iron-clad grip on trackpads because it doesn't seem as if anyone else uses them for phone navigation. I can't see Windows 10 being useful on a 7" (or smaller) display. I've tried some of the 8" tablets when they were on W8 and were impossibly difficult to use. Slider bars and other buttons are simply too small and I don't see a stylus being the answer.
Ideally the idea of Win32 on ARM will catch on, and companies will make their desktop apps catered to it, if not going full UWP app.
I could totally see desktop apps already in the store, such as Spotify, Arduino, making their desktop apps more touch-friendly and better scaling.
A lot of desktop apps already adjust for touch navigation. Chrome (I think), Office (although that is a MS product), Adobe apps, Plex, Steam has big-picture. That covers a lot of people's most commonly used desktop apps.
Even still, the convenience of having a pocketable device might outweigh the inconvenience of poor usability for some people.
Not to mention you can still plug in an external screen, mouse, or as you said, a stylus, and it's perfectly usable in that case.
They also DO have an on-screen touchpad already. I think they added it in the Creators Update. Could use more polish, but it still gives you a usable cursor without external devices.