Vernacular and colloquialism are all well and good with spoken english. But the beauty of english (to me at least) is its expressiveness and ability to be clear, concise and descriptive, and imaginative.
If you carry over 'slang' into the written word you loose all sense of context and meaning. It is not evolution, but degeneration. Nothing is added as a benefit to the whole of the language in general terms, but much is lost or taken away through ignorance or plain laziness.
Evolution of language, such as the online verbiage as we see here every day, would be such things as 'lol' or 'omg' 'wtf' - less a way of talking and more a means of relaying more complex information and common phrasing without the need to write it out long hand... it's called an acronym. But these are subjective to common (regular) users of the internet and not incorporated into the language at large. Informal speech and writing.
Dissolution of language to the extent that meaning, and therefore understanding, is lost is not a good thing - replacing descriptive words with those simpler and less versatile, because of slack teaching, is part of the reason why we now have a good proportion of our youth who have no grasp of communication above the most basic, vulgar, grunting.
I have a reasonable grasp of spoken and written english, and while I find it slightly annoying when grammar and comprehension are ignored on forums etc (more for the fact that I have to then guess at the meaning, than any real hatred), what is most unfortunate is having to say something again in a simpler, more pedestrian way, when the person I am speaking to does not understand due to their lack of education. Depending on the individual I either get a blank look, or they seem to think I am taking the ****; the suspicion being that "usin' big letters innit" is deliberate to obfuscate their understanding. It is not. It's just the way I was taught at school and by my parents.
Sadly, the lowest common denominator appears to be the standard of teaching these days.
I am guilty of assuming that a lack of correct language (written or spoken), sometimes implies a lack of intelligence or education, often both, when applied to some younger people.

How you speak and write can be deemed illustrative of how you
think.