It might just work. Often steel threadless steerer tubes have the same thickness as threaded. Sometimes they are not. Take a measurement and see if it is the right size. If it is, then it will work.

I'd be careful threading the steerer tube if you want to put a locknut on it for aesthetics. Just thread it enough for the locknut to go on, but not all the way to the clamping area. It might be hard to find the right tool to thread the steerer. I have not checked all LBSs but I have heard that most only have the die to chase the threads or the one to extend the threads, not the one to start the threads. A frame builder might have the correct tool.

I agree with you, a good looking quill stem is much better looking than any threadless stem. I want to find a quill stem that has a pop top so that I can buy the bars I want. Right now I have one of those adapters to be able to use the threadless stem on one of my bikes. Just not the same. But, so far, the only ones I can find are welded and I hate those more than threadless.