I had read about people trying this on backpacking forums. So, I decided to try it out for myself. How many times did I wear my merino wool shirt without washing? The answer - 10.
10 times and yet no odor. No itches either. It was as if I'd picked up a fresh shirt each time I went for a run.
Could I have gone longer? I think so. Unfortunately, the weather wasn't cooperative. The winter rains set in, which means less time in between runs for the shirt to dry out completely. I could've let it dry out over a few days but I didn't happen to have too many extra shirts to alternate. Moreover, if you don't let it dry out completely, there is a little bit of a funky odor. Maybe next time, I'll shoot for over 10.