I'll say this. I got an Index when they first came out. Any kind of teleport motion was perfectly fine day 0. But the moment I tried smooth locomotion, it was instant sickness. Like literally walking across the room with smooth loco and had to take off the headset and lie down for half an hour. After that, I forced myself to do about 10 minutes of smooth locomotion every day. At the end of the week, I ended up playing a smooth locomotion game for about two hours without even really noticing. The day before, I got sick at fifteen minutes, but all of a sudden VR just clicked and I've never gotten sick since. Not even after going long (6 month) stretches between playing any VR games.
Now, that might not be a cure for everyone, but if someone is having motion sickness issues, I recommend just powering through it little bits at a time for a few days.