public abstract class VariableReference<TBase, TScriptableVariable> where TScriptableVariable : ScriptableObjectVariable<TBase>
{
    [SerializeField] private bool useConstant;
    [SerializeField] private TBase constantValue;
    [SerializeField] private TScriptableVariable variable;

    public TBase Value => useConstant ? constantValue : variable.value;
}

[Serializable]
public class FloatReference : VariableReference<float,FloatVariable>
{

}

public class TestBehaviour : MonoBehaviour
{
    public FloatReference floatRef;

    private void Start()
    {
    }
}