I'm merely curious, as when 3D movies came out a major complaint against them was that people got sick from watching them.

From my very thorough research (googling "3D movie sick", and looking at the dates; all from the period 2010-2015) this doesn't seem to be a big problem any more. Now this could of course also be because people have just accepted that it is not for them, the people who get sick don't talk about it any more, or people in general have just moved on from 3D, but it does make me wonder. Could the motion sickness not also just be a temporary thing for VR?

The people who get sick from them don't go to them anymore. That's why it was "temporary". Kids finding out they get sick from 3D don't post about it on the same social media adults use.

But in terms of viability, it is also a matter of degrees: do more than half of your users feel sick after using your product, or only very small percentage?