Aside from the well known problem of discoverability, there are two things that kill me about VUIs:

1) Slowness. Not just the lag before you start talking, which I presume will get reduced to basically nothing, but the speed of the assistants speech and their verbosity. I wish you could make them talk faster and also enable some sort of “terse mode”

2) Chaining. I wish they’d listen after the last action for a few seconds and in that state be able to act on things like “do that again” or refer to the main subject of the last answer like “...and what movies was she in last year”?