Well, I think you guys are missing the point. I am talking about groups in DC, ie members have opted in and are all using DC. Not the use of DC as a general mail client - although I don’t see why it could not be used there as well. I do not want to see any gratuitous “marketing” messages.
In the former scenario, the poll can be on anything on when to have a meeting, what to discuss etc etc. In other words, members are already committed to the purpose of the group and its activities.
Again, Threema, a privacy-dedicated e-mail client has that feature, as does Telegram. Possibly others as well which I do not know anything about.