"Expiring votes requiring revoting twice a year keep the legacy votes from perpetuating witnesses not currently active."

Good thinking. Otherwise, witnesses are like Banks, where you pick one at 18, and somehow, 50 years later, you still have the same bank through sheer inertia. So many people are like this.

And that bank definitely is gonna take advantage of you because you have no agency. You are a passive consumer.

Basically, your proposal amounts to a call for "elections," and in a democracy, that's not a bad idea. :)