I think that the easiest way is to create an instance and collect votes.
Or even just make a little tool "hey I wanna stalk this (political / porn / whatever) community, run an endpoint for me that's subscribed to it and give me a little report of who all is upvoting stuff in it".
I sort of assumed that the process that downloads a community's history when it's first federated also includes the identity of all the past votes (I feel like it has to be that way in order to make sure we're not double-counting votes during federation?), but that's just uneducated guessing.
I think so too. I have already been part of a few conversations with users who have just discovered that this is possible. I think that this transparency is something that the feature wants to achieve, but it is important to publicize it to avoid surprises.
Honestly I think that for new users the upvote / downvote buttons should literally pop up a message on every vote that says, "Hey! Due to the nature of the fediverse your upvotes and downvotes are semi-public information!" until you check the box that says "don't show me again."
Personally for me I don't have a problem with people being aware of my votes, but that's partly because I assume it's semi-public knowledge in the first place. I feel like enough people are unaware that taking too close a look at votes might be a privacy issue, but really the issue is the unawareness, not the looking.