I do not support this request by any measure nor for the time being nor in the foreseeable future for the following reasons:
1. 99.9% of all buildings being modelled in CAD or BIM can be done quiet fine with Meshes (in your case it's the Morph tool), and the rest Nurbs can become a necessity for practical reasons.
2. Nurbs from a computer processing view would add an exponential high load on the computer resources.
3. What you're asking be be solved by 2 ways ...
3.a. You create the Morph model in a separate ArchiCAD file.
3.b. You use a computer clay sculpting program that can export the result to ArchiCAD.
A good friend of mine have once told me that I´m so brute that I´m capable of creating a GDL script capable of creating GDLs.