I understand that you want to see the form as you make the rail but you can always just edit the curve points in MOI after you have made your sweep or revolve and it updates the surface fairly quickly.

Amapi and Hexagon spoiled a lot of people by using their Nurbs and dynamic approach to poly modeling. I use both and have Amapi 8 and I am sure it would have been received very well if it had been released. No other poly modeler really was as versatile in how you can create forms using Nurbs techniques (sweep, extrudes, lofts)