Somehow, this West Coast abomination has crossed the Pacific and ended up in my country of residence. Like uptalking, this interrogative-declarative is a petty demand for attention. Not content to merely endorse a statement with a "well said!" or "hear, hear!", the yammering fuck that employs "I know, right?" is asking for their affirmation to be affirmed. Congratulated, even.
You can call this "hypersocialisation of conversational roles" whatever other buzzwords you use to get attention from people you're trying to flatter or excuse with your disposable thesis, but you're wrong, and it's really just the mark of an irritating cunt.