I think we can go several decades further back than that. Think about how many products, services, and retailers spelled "and" as "N" or "right" as "rite", and so on. Even ToysRUs is in on the subversion. No, it goes back a lot further than recent pop culture.
A lot of this is a sort of extrapolation of Grice's conversational maxims, but in written form. In other words, by diverging visibly from how something
should be, and is expected to be spelled, one conveys surplus meaning in a sort of "hidden code" form. So use of "-n-" instead of "and" is intended to convey "we're not like those
other products or vendors; we're on
your side". There's a fascinating semiotics of deliberate language corruption. I was introduced to it by this book:
Cool: The Signs and Meanings of Adolescence: Danesi, Marcel: 9780802004673: Books - Amazon.ca
I've been blathering on for years about what I call the "adolocentric society", that has increasingly adopted the norms and objectives of adolescence as some sort of de facto standard for how we should behave, and what we should aspire to. Sociolinguists will note that a big part of how adolescents talk is intended to differentiate themselves both from their parents and from other social groups. In other words, misspelling and misuse of words ("that's really
sick") has the purpose of aligning oneself with age-mates and differentiating oneself from older persons. It becomes their "secret code" for communicating with each other in a way that an older generation wouldn't (and
shouldn't) understand. The purpose is ostensibly to forge a sense of identity through group membership. I.E.,
"We understand each other, so we're not like
them, which means I know who I am - I'm one of us and NOT them". It's an understandable and important aspect of adolescent development; likely observable for centuries. It becomes problematic when it extends well beyond one's teens and early 20s and is carried over into one's 40s and 50s, which is the trend and scenario I refer to as "adolocentric".
But, all of that being said, I think it unwise to attribute the decline of "proper" language to any single thing. This is a mountain being eroded by many different factors on all sides.