My contention is that I don’t believe this tool works very well now or that it ever will.
There are CAD programs that cost more than ten times what Rhino cost that don’t do it very well so it seems like a poor investment in development resources for Rhino to even try.
That said, There is a lot that Rhino developers could do to assist users design tooling and created good well-behaved functional parting surfaces.
In the vast majority of cases where an irregular parting is needed the best way to get a good parting surface is to modify the part to conform to a good parting surface rather than trying to make a parting surface conform to a part that is not designed well. Take an exhaust manifold for instance
At the parting line the draft angle is zero and very tiny changes to the shape of the part geometry in that area can make huge changes in the shape of the parting surface . Move a control point 1mm and the parting surface can change by 10mm or more. Rhino is well equipped to do that kind of editing.
Draft Angle Analysis is one of the most important Rhino tools for designing tooling.
When I reported bugs that were introduced in Rhino7’s Draft Angle Analysis it was pooh-poohed and ignored. Now Rhino8 had the same bugs that were introduced in Rhino7.
In general fixing long standing bugs would help many Rhino users, not just tooling designers.
History as implemented by Rhino is also an extremely useful tool in designing tooling. Having history enabled for Silhouette, draft curves created by Draft Angle Analysis and the the Fin command would be useful additions.