I think it would be incredibly cool if you could click anywhere on a flat surface to convert it to a curved one. The tool could work similarly to "add edge loop" in blender.

When you click on the surface to add your "edge loop", all it would theoretically need to do is increase your surface degree by +1 degree, so then you have a sort of edge you can then push or pull to your liking. This would prevent the need for drawing curves and extruding them in order to get a curved surface. You could start with a block and then shape it as you like with as many "edge loops" as you want.

Ideally to ensure smoothness, it would only increase degree and not segment the surface, but a segmentation checkbox could be added as an option for the tool.