1. Make the player's mass scaled with size so props won't move as much when shrunk and heavier props will move when bigger.
2. Allow scaled up players to crush entities below them just like in Shrinkinator.
3. Scale damage by size.
4. Scale health by size.
5. Add an option for fall damage when shrunk (basically make distance for fall damage relative to size)
6. Add an option to automatically go back to the size you were at before you died.
7. Add an option to have your ragdoll be the same size you were when you died.
8. Make it easier for ragdolls to crush you when shrunk.

Feel free to add to my suggestions by commenting as I might add them to the main list.