While it would be a neat thing to have, the question is what would really be the benefit of it?
I mostly use icons like these to show what champion I am currently talking about and the icons are recognised by the great majority of people, so it can serve this purpose.
You can argue that you can use these icons you are requesting if you want to discuss a specific skin of a champion, but I kinda doubt that many people would recognise all these skin icons in the first place, which means that the use of these icons would be majorly hindered by that.
So it would be quite alot of effort, while not really fulfilling any real purpose, except that it would be cool.