This makes me wonder what could be done with, say, a bluetooth earbud and a smartphone, both of which are rather less conspicuous than Google Glass. Not quite as good as connecting straight to the auditory cortex, but still. The first thing that comes to mind is trying to get GPS navigation to work on a System 1 rather than System 2 level, through subtle cues rather than interpreted speech.

[Edit: or positional cues rather than navigational. Not just knowing which way north is, but knowing which way home is.]