I think the primary feature of Nostr is that this kind of consensus is not possible unless you agree to query the same relays.
Discussion
Which is kind of the solution for these polls, I guess. Every poll can signal a relay that will be the authoritative one for counting the votes, and everybody tries to vote on that one and query responses from that.
Whenever we get more segregation between relays it will be nice to be able to browse different results across different relays to see how different communities vote differently on the same poll.