I would worry about clamping to threads. Instead of the stem tightening on a nice smooth piece of metal with lots of contact area, you're limiting your contact to the ridges of the threads. While the threads would probably smash down with enough clamping force, you'd then have a smaller diameter at the stem than the original fork. Might make keeping the stem tight problematic.
Did it and still doing it on Sir Walter. Niot a problem and have a couple hundred miles on it. The threads don't smash down, as the last time I changed the stem they were still very much intact. Why did I do it? It was originally a cheap-as-i-could-build-it project and I had numerous threadless stems and an extra HS in the box and the fork had enough length to the steere tube to try it. Have not found a reason to change it yet.