I have never encountered this.
- But it would be nice to be able to retain the original fork... In lieu of finding another longer fork &/grafting on the steerer from it, your frame builder's suggestion might well be a viable option. That is, I assume your frame builder knows what he's doing. If you do go that way, it would be best to measure twice to ensure you don't take too much off the top, and risk having the rear edge of the skirt from the threaded top race in contact with the TT.