An attribute for MonoBehaviour's that restricts assigning in the editor to MB's deriving from a specific interface.

InterfaceAttribute.cs

/*
*   Author: Harshdeep Singh, https://github.com/h-sigma
*   Year: 2020
*   Description: An attribute for MonoBehaviour's that restricts assigning in the editor to MB's deriving from a specific interface. 
*   Use:  
*   [Interface(typeof<IHealth>)]
*   public MonoBehaviour health;
*   Note: This hasn't been bug tested, and it is a very simplistic way to do the job. If required or requested, I may choose to improve it.
*/

//place this in regular scripts directory

public class InterfaceAttribute : PropertyAttribute
    {
        public Type interfaceType;

        public InterfaceAttribute(Type interfaceType)
        {
            this.interfaceType = interfaceType;
        }
    }

InterfaceAttributePropertyDrawer.cs

using System;
using UnityEditor;
using UnityEngine;
using Object = System.Object;

//place this in an Editor folder

[CustomPropertyDrawer(typeof(InterfaceAttribute))]
    public class InterfaceAttributePropertyDrawer : PropertyDrawer
    {
        private InterfaceAttribute attr;
        private Type               type => attr.interfaceType;

        private MonoBehaviour linkedMb;

        public override void OnGUI(Rect position, SerializedProperty property,
            GUIContent                  label)
        {
            attr = attribute as InterfaceAttribute;
            if (attr == null || type == null) return;

            var mb = property.objectReferenceValue;
            var obj = FetchMonobehaviour(mb);

            EditorGUI.BeginChangeCheck();

            GameObject gameobj = obj == null ? null : obj.gameObject;

            var l = gameobj == null ? property.displayName : property.displayName + $" ({obj.GetType().Name})";
            
                
            if(EditorUtility.IsPersistent(property.serializedObject.targetObject))
                gameobj = EditorGUI.ObjectField(position, l, gameobj, typeof(GameObject),
                    false) as GameObject;
            else
                gameobj = EditorGUI.ObjectField(position, l, gameobj, typeof(GameObject),
                    true) as GameObject;


            if (EditorGUI.EndChangeCheck())
            {
                property.objectReferenceValue = FetchMonobehaviour(gameobj);
            }
        }

        private MonoBehaviour FetchMonobehaviour(UnityEngine.Object obj)
        {
            if (obj == null) return null;
            switch (obj)
            {
                case MonoBehaviour mb:
                    if (type.IsInstanceOfType(mb))
                        return mb;
                    else
                        return null;
                case GameObject gameObject:
                    var candidate = gameObject.GetComponent(type) as MonoBehaviour;
                    return candidate;
                default:
                    return null;
            }
        }
    }