Can Qualtrics be used for polls, in which audience can add choices?

I can think of a way to make this work using a Contact List. you would have to do a Contact List Authentication and a Contact List Trigger. You would want to set a limit though.

Idea 1: First query everyone for what movies should be in the top 100. Then after a set date, resend to all voters with the list of choices to pick the top 5
Idea 2: More to what you are doing... Create your list of choices and include an Other (or add it as a new question - "Who did we miss?"). The last N choices in your question would be empty (and therefore not display). Pull these choices from a contact list. As people add "what you missed" choices, they get added to the Contact List via the trigger. They would then show for the next person. You likely would have to set a limit when reached you stop allowing additions or the list could become unruly (way too long?). Happy to step through it with you if you want.