Earlier quoted context omitted.
The problem with FreeCAD and every other free/open source MCAD project of note is the Open Cascade kernel they are built on. While Open Cascade is fairly mature, it has dealbreaker issues in a few key areas: fillets cannot consume connected faces and may fail for a number of other reasons, cylindrical and spherical faces require seams which often cause issues with boolean operations, and shapes like helixes are also…
On a scale from "big chunk of work" to "complete rewrite", how much work would it take to fix those issues in Open Cascade?
Some of these issues are long standing and really hard to solve. Someone could probably defend an entire PhD thesis on “redesigning the topological representation to eliminate seam edges” without making much practical progress