In a move that should be a surprise to no one, Mastodon has finally merged in the feature capabilities for federated polls. According to Eugen, there currently isn’t a UI component for creating polls yet; they can only be created via the backend.
That said, if your server already has a compatible polls feature, you can participate in any polls coming from Mastodon. The API reference has been updated, so expect support for polls to get adopted by various mobile and desktop clients fairly soon.
The Pleroma project are already considering how to support this new feature so that it remains compatible between both projects.