The short version:
No, they're not interchangeable.
Quill stems rely on the top half of the headset to set and hold the headset bearing preload.
And you can only do that with threaded forks that take threaded headsets.

For aheadset/threadless, headset bearing preload is set and held by Star fangled nut/compression plug + top cap + stem. And you can't get that functionality from a quill


The long version:
With a quill stem, the steerer tube of the fork is threaded at the top, and protrudes just far enough past the top of the headtube of the frame to make room for the top headset assembly. The top headset assembly has a cup that's pressed into the headtube, then a cone that's threaded onto the steerer tube and then a locknut on top of that.

(Maybe a washer or two, but lets ignore them at the moment)

The threaded parts, cone and locknut, is what sets the bearing preload.

The quill (stem) is then inserted into the steerer tube and locked in place by a sliding wedge at the tip of the quill. You can pull the stem out w/o interfering with the headset bearing preload.


With a threadless/aheadset stem, the steerer tube is smooth, and extends well above the top headset assembly.
The top headset assembly is also smooth. It centers the steerer tube in the headtube, but doesn't really grip it with any important amount of force.
Headset only has not chance of setting or holding the headset bearing preload.
Then the stem is placed over the steerer tube (add spacers as needed/preferred). Bearing preload is set by the stem being forced downwards courtesy of the top cap and an anchor inserted into the end of the steerer tube. Usually something called a star fangled nut, but there are other options available.
Then the wraparound part of the stem is tightened around the steerer tube to lock the preload in.

So, if you were to try to use a quill stem in a threadless fork, there's no way to set the headset bearing preload any more. There is no mechanism allowing a quill stem to be pulled down, while bracing against the top headset assembly.

If you really insist, there are workarounds.
It's possible to set the preload by external means. Big C-clamp, threaded rod through steerer etc etc, then use a properly sized seatpost clamp around the steerer tube to lock the preload in.
If your steerer tube can take the expansion force caused by the wedge, you can then install a quill stem and ride happily ever after.

But why?

The only practical advantage of quill stems is that they allow for greater/easier adjustability of bar height.

And unless it's a loaner, bike, people tend not to touch that adjustment very often.