Are you talking about voting by BTS holders that will influence the behavior of the DAC itself? Or are you talking about voting for things like polls or government elections?
The only thing I have heard about so far regarding DAC-related voting is the system described by bytemaster to vote on whether to activate hard fork features on the blockchain, which only occurs if there is 75% BTS approval.
If you are talking about the type of voting intended by the original Voting DAC, then I just think of them as a system that allows you to determine whether an anonymously submitted ballot counts as valid for a given election or not (with equal voting power behind each ballot for initial simplicity). Once you have that basic framework, the clients can implement any kind of voting method they want on top (FPTP, IRV, STV, Range, etc.). You can invent all kinds of interesting consensus requirements. The client could also filter ballots based on the block in which the ballot (or rather ballot hash) was submitted in so that you can ignore any ballots that came after some deadline. None of that validation logic needs to be done on-chain. Also keep in mind that if the ballot information becomes publicly available as voters submit their vote, you cannot prevent clients from analyzing the results live. If you don't build it into the default client, people can make and use other clients that do calculate the results live. The best you could do if you for some reason really wanted to hide the live updates (which I personally only agree with for scientific studies but not for any public elections) is to hope voters use a client that is designed to commit to a hash of their ballot that is submitted to the blockchain by some deadline and then only reveals the actual ballot contents to the public after the deadline.