I'll just give you my thoughts on one of your questions.
I have seeen a considerable change in my lifetime, and I frequently read complaints from people my age (mid-60s) about the 'dumbing-down' of language. People have been making similar complaints for over four hundred years, and will doubtless continue to do so. The language still changed, and will continue to do so.
I would not be surprised if such forms as , for example, wanna, gonna, gotta and oughta (for want to, going to, [have] got to and ought to) were one day accepted as written forms in even formal English.
By the way, pls is still not approved of in this forum - yet.