This could get serious.

Prescriptivist? An awful word, as are many which seem to say something but which are just labels. No teacher operates in a vacuum, cultural or otherwise, and to deny that a teacher can give opinions on the general "acceptability" of something would be sad.
To paraphrase; every teacher is entitled to their own opinion, but they aren't entitled to their own set of facts.
I define acceptability as something that most people, especially those who give some thought to a subject, think is "a bad idea". To teach anyone learning English that the small i is a good idea is just ridiculous.
I'd say that, by and large, we're on the same page, Davy. It is certainly not appropriate for certain registers. But it's a done deal for some areas of language use.
I will always refuse to agree that a language can be determined by the technical operation of a mobile phone or the rush to say something in a chatroom. This has nothing to do with formal/informal usage. It is sheer laziness and disrespect for good communication. And yes, I know that any adjective such as
good can be analysed to death. Sometimes things just are good or bad.
Language change is neither good nor bad. It is completely neutral, indifferent. The only thing that determines language change is usage.
I also feel that to quote any one person, whether they be a poet or a politician, as any sort of validation for a point is no proof. They make their choices as do we all.
Precisely and the choices being made in chat rooms, PMs, emails and the like is towards a simplified English. If it didn't work for what language is all about, communication, then something else would be found. But hey, it works.
Is it going to take over in the newspapers, academia, no, of course not.