Could use the mud to clay conversion to convert dirt into sand (or gravel to sand) ?, that would be as close to vanilla as possible.

It would, however it would also mean that all Mud -> Clay farms can be used without modification to turn Dirt -> Sand. This would be pretty boring imo. I prefer to add new vanilla-like mechanics instead of just reusing the current vanilla mechanics. Maybe I can add this as a default-disabled option for people that prefer this method.