When he teaches this during class he does not refer to internals. And he does not use words or terms that can be found when talking about Internal Training.
Nevertheless: Feeling this, watching him when he just does it with his uke (not teaching but practicing himself) and teaching and practicing this at home myself made me listen up, when I read about internal training here.
... I think there is some connection ...
but I don't think, videos of Endo sensei will help to get into internal practice.
It's the other way round: When you get an idea of internal practice you will find things when practicing with Endo sensei or with some of his students.
I think that you make a very valuable point. If you are lucky enough to work with somebody who can accurately explain, teach and get you to do some internal stuff (eg.- Dan Harden) you suddenly become aware of what some people are doing. That is exactly how I have been able to decipher and better understand what Imaizumi Sensei is doing. It is not as though some people do not have some degree of internal "abilities/skills", it is that so few people can accurately describe it, teach it and help you do it.