When I was working on adding voting to lemmy (I never finished it) one of my features I wanted was exactly this. Essentially locking down votes to your instance, meaning you have to have an account in the instance to vote and the votes won’t federate. This would make it so that users of the instance could make decisions without brigading from other instances.

One thing I do beg you to add: 3-2-1 voting and STAR voting. We really need to stop using plurality voting for things.