Make users list autocomplete instead of dropdown

Hi, I think in the old module (Zmove's) the list of Users to include in the coupon was an autocompleting text field, not a dropdown. The dropdown is a little more resource-intensive than an autocomplete would be (and therefore takes longer to render on the page), especially on our site which has tens of thousands of users.

If you could make this autocomplete I think that would make more logistical sense. Thanks!