I have stumbled across SoftEditGrips and it is exactly the tool I have been looking for. It is the nearest equivalent to Fusion’s soft modification function that I have seen.
There are a few improvements I think could be made:
It would greatly increase the functionality if I could change the gumball alignment when selecting grip(s). Currently it is limited to Align to World, which does not allow me to move a grip along the surface normal.
Furthermore, the visual overlay for the falloff could be improved. It would be helpful if the heatmap (or colour) would change depending on the Mode selected. For instance: for Mode=Smooth, I expect the overlay to falloff; but for Mode=Constant, I expect the overlay to be the same heat (or colour) across the whole radius.
Otherwise, a tool with fantastic potential.