I think he partly got the prediction right, that usability would be big differentiator. Apple and MS over the following years had big efforts focused on consistency in their interfaces and we had what many consider a golden age of UI usability, at least from a consistency standpoint. I think what happened next is that two things came along and basically reset the state of UI design back to zero: Mobile and the web.
Both platforms were so radically different that Apple and MS UI guidelines were useless. We got a horde of web and mobile designers experimenting with all sorts of novel interfaces. Experimentation is a great thing but consistency has definitely suffered. I've long thought there was big money to made by somebody wrapping up a complete linux distro, with a set of common applications (libreoffice, et al) but putting in the (very significant) effort to standardize _every_ interface, write good manuals and provide customer support. Sort of like the service that Red Hat provides for servers but with a desktop focus. Maybe they couldn't eat MS's lunch, but if they could demonstrate big productivity gains for businesses, maybe they could.
In the last decade I think we've seen the (much needed) injection of artistic talent into the UI design space. UIs today are much more beautiful than in 1995. That's because businesses realized that users value beauty and hardware improved to the point where more visual effects could be provided without sacrificing performance. In the next decade I think we'll see a resurgence of focus on accessibility and usability centered around design guidelines that coalesce out of consensus in disparate communities rather than corporate policy. I think especially that as Moore's law continues to flatten out, and network connection speeds start to platau we're going to see a renewed focus on responsive UI design and application performance. I am excited about these trends and feel optimistic about software design going forward.
Too bad Nielson was totally wrong about customer service though. :-(