How could he have Bijuu Mode...Bijuu Mode in Naruto's case means that he cooperates with Kurama. Minato does not have Kurama, just half of his chakra...
Pretty much, yeah.
Nice theory!
And about a triangle it makes sense
KM Minato.
The patterns are identical to KM Naruto. Minato just happens to be wearing a cloak.
^^This is it in a nutshell^^
This is entirely plausible. For me I believe, since Yin is the spiritual part, there is no Bijuu entity, just the chakra. Naruto has the Yang which is Physical and allows him to host the physical portion of Kurama. Also, the seals on both are flipped, with Minato's being upwards and Naruto's downwards.
The way I see it: The benefits Minato has are more akin to KCM, but because he is in an undying body that doesn't feel pain, and the chakra he is hosting isn't a physical entity, he doesn't need to "master" or cooperate with it like Naruto did with Kurama; Hence why it can be called a mixture of both.
I believe it to just be a more advanced version of the seal that he put onto Naruto or he has more control of the KCM than Naruto was. Nothing on him says BM other than the seals on his hands. The spikes on his head is his long hair that sits on the sides of his face. The magatama looks like it is on any clothes that you wear, he just so happens to have a coat already.