Being able to convert fabrication to generic parts allows similar process within Revit that Fabrication CADmep has had for years called design line. A perfect example of when we would use this feature is if we draw a system as Carbon Steel and word comes down that it needs to be Stainless Steel. Currently our options are incredibly limited (and actually lead us to find a bug). We can either delete and redraw (OH HELLZ NO!) or we use Revit's awesome ability to "Revise It" and change the type. Since our systems often carry multiple types (PVC/Cast Iron, or Carbon Steel/Stainless Steel/Copper, etc.) we have this option within Revit. Here though is where we found our bug. Changing the type did not change the actual material and through the outside diameter of the pipe off, it wasn't anything outrageous but enough to be noticeable upon close inspection. Further it pushes this incorrect material down the system as you draw so even new Stainless Steel pipe has a material of Carbon Steel. Luckily we don't report the material for our BOMs or tags, however it is used by our hanger calculator to determine weight and spacing and this could cause a major problem.
If we could take our Carbon Steel pipe, convert to generic Revit pipe/fittings, then convert back to Fabrication pipe using Stainless Steel this would resolve the issue. Obviously it's better to do it right the first time, but we all know how these things can change part way through.