I'm not sure your argument is valid. How is the decision made to convert x/y to fraction form? Is it white-space/punctuation+whitespace on either side? If that's the case, then: xxx/yyy will never become fraction form; however, x/y and x/y. (as in the end of a sentence) will.
But this does not work this way -- it seems it just blindly consumes char before and after / and converts if this fraction has a glyph in the font. Also, what you suggest is hard to implement since there are numerous localisation-dependent options what a whitespace/punctuation is and where to search it.