So many things come to mind. In addition to the training tools xandros9 mentions, I see so many places where VR/MR/AR can expand into. I don't necessarily mean today's hardware, but looking beyond the curve where MR is built into every computer, tablet and (perhaps) pair of glasses being manufactured. The standalone headsets and the leap motion announcement give a hint as to where things are going
Already, architecture programs let you upload your CAD drawings so that you can experience your structure before it's even built. That's huge! no physical model building. There are real estate companies in my area that are using VR to allow prospective buyers to tour residences at their convenience.
As you say, HoloLens will be great for some business applications as well as being awesome for museums, art galleries, public displays etc.
For me the biggest and most surprising use of VR has been in content creation. Sculpting programs, painting programs and (my absolute personal favourite) animation tools like Mindshow let me create an animated shorts of whatever my mind can imagine at the time. Like this little short
https://www.youtube.com/watch?v=WNNksPypORU You literally hop in and act out the character in real time.
IMHO there is a lot of fun to be had with "gaming", but we're just starting to scratch the surface in creating experiential and content creation tools.
That's my take on it, for what it's worth.