Scooper

Here's my take FWIW.

If the steerer is brazed into the fork crown with brass filler, removing the steerer using heat is likely to compromise the structural integrity of the crown. If it was silver brazed, there's less of a risk. So, depending on how it was brazed will determine how to proceed.

If brass filler was used, the old steerer can be cut off flush with the top of the crown and the crown hole precisely line bored in a well equipped machine shop to remove the remnants of the old steerer without using heat. A new steerer can then be brazed into the bored hole in the crown.

New threaded 1" steel steerer tubes of various lengths are readily available from Nova and other suppliers at low cost (~$20), but whether this is economically feasible is a big question considering the machine shop costs and the cost to repaint the fork.

My guess is that not many framebuilders or machinists would want to tackle this because of liability issues.