With regards to the video's gripe with Obito interacting with Kakashi from beyond the grave, I'd like to point out that this situation is somewhat unique, since Obito had been infused with so much of Naruto's Rikudou chakra. I believe that this chakra provided the "link" in our world (which normally wouldn't be present if one had died) for Obito's chakra to return to from the pure realm. We see Obito coming out of his pile of ashes, so clearly he wasn't just ascending from the heavens, so to speak; he was tethered to those remains. I believe that the reason for that is the chakra Naruto gave him.
We know that Hagoromo is a being who exists between the Pure Realm and the living world; that's why he's able to bring in the spirits of the previous Kage to perform his massive summoning jutsu, and why he has survived for so long merely as a mass of floating chakra. Indra and Ashura work in much the same way; they exist as chakra beings, choosing new hosts to "reincarnate" into and granting those hosts their formidable chakra.
In a sense, the conditions were met for Obito to borrow Hagoromo's ability to "reincarnate" into Kakashi in much the same way. However, unlike Hagoromo, Ashura, or Indra, Obito needed a tether (the Rikudou-infused ashes) to pull it off. At least, that's my theory of how this feat operated within the rules/precedents of Kishi's universe. And of course, it's all based on the questionable reincarnation/ghost principles introduced in the last 30 chapters of the series, which may be "asspulls" in and of themselves.
