I don't see anything inherently wrong with nursing an 8-year-old who wants to nurse, I suppose, although I certainly don't think I'd get that far myself. If the child was nursing a lot, I suppose I might worry about her permanent teeth coming in wrong, but I don't imagine most nursing 8-year-olds (if there are enough of them to actually make a generalization) nurse often enough to cause a problem.
But, if you think you've seen everything after that video, consider this story that I must admit is secondhand to me (and thus thirdhand to you):
A friend of mine, when she was younger, was traveling in India, and feeling very full of her cultural tolerance. During her trip, she was once on a train, sitting across from a young mother who had a little boy with her who appeared to be about 6. When the young lady started nursing her son, my friend was filled with pride at her own open-mindedness. After all, she'd never seen a school-aged child breastfed before, but she wasn't shocked! After a few minutes, however, the child sat up, leaned back comfortably in his seat, and lit up a cigarette.
The lady who told me that story, I feel, has indeed seen everything in the world of long-term nursing.
Nealy
mama to T, 5 (Ordinary Parents' Guide to Teaching Reading, Zaner-Bloser Handwriting Level K, and Saxon Math Level K); L, 2 (a co-op preschool-goer); and O, EDD 12/20/08, whose school is the womb.