As an all-purpose
question tag, it serves a purpose in English, particularly in varieties of the language that are influenced multiculturally, which follow a more typical tag formation pattern, often found in other languages (a one-word tag, if you will). It gets round, to a certain extent, the complex (but fully-functional and really quite elegant) nature of agreement with regard to tense, aspect and modality of question tags in standard English.
In 100 yrs time, I predict that it will have earned its place in the grammar books, alongside (but not replacing) standard question tags. Innit.
