She Bop

In a lecture that I attended today given by Professor Emeritus Sandra McKay, a sociolinguist from San Francisco State University, she discussed some of the implications that English becoming the paramount global language might have for teachers of English in places like Singapore. One focus of this discussion was on the sort of feedback that teachers should be giving developing student writers in light of contemporary " sociolinguistic theory" that posits that all varieties of English have legitimacy.

Generally, according to McKay, one important issue is this: It is easy to see that new lexical items (think new base verb forms, for instance, "to google" and "to sms") appear then quickly gain global acceptance and legitimacy. Similar innovations in grammar may develop, such as the way that people worldwide who use English as a second language (and the number of these far outnumbers that for whom it is the first language) often drop the "s" on simple present verb forms in the third person singular: she bops >>> she bop. However, acceptance of such a change in grammar is very slow to develop. In fact, many teachers would consider this an "error" and would make mention of it in feedback to the student.

The question sequence then is this: What should a writing teacher do when encountering such a "drop" of the "s"? Should he or she (we!) accept this drop, seeing it as legitimate, or not?

Let's add a very real context to this: What should I do if and when I encounter an occurrence like the following in a student's blog writing?

I write like this and she write like that. 

I can give McKay's view, but I'd like to hear yours first.  Please give me your opinion and explain why you feel that way.