The fork crown area has much greater forces acting on it than the stem, you need more strength there not "corrupted" by a cut out & clamp.
The only purpose I can see is if the rider is likely to swap over their forks often, but wishes to keep the bars setup the same. But it seems to me that fiddling with different stems occurs more often than switching forks.
Dont get the clamp on fork idea.
The fork crown area has much greater forces acting on it than the stem, you need more strength there not "corrupted" by a cut out & clamp.
The only purpose I can see is if the rider is likely to swap over their forks often, but wishes to keep the bars setup the same. But it seems to me that fiddling with different stems occurs more often than switching forks.