"Of the two, B is a more prudent way of making property prices sane again."
Maybe if you taxed unused land. Otherwise that tax will end up increasing a resident's rent/mortgage substantially (as it's a perpetual annual expense). So really, you'd have to tax way above what a normal person can afford (average US household about $75k, so $7500 is 10% gross), and that still wouldn't be much of a disincentive to the wealthy (ignoring the fact the the market would collapse because normal people can't afford to buy it from them nor pay the rent).
Now if we did tax unused land, then we are reducing conservation and incentivize development. This is a major concern for some areas, especially around loss of agriculture land, riparian buffers for water quality, etc.
If we had work that was more distributed, like remote is for IT, then it's possible the effects of all the capital flooding a handful of markets would be diluted by spreading it across numerous others. A generation or two ago we had many small cities with industrial or manufacturing jobs. Now it seems many of those cities have shrunk while the national population has grown, mostly concentrating in specific metro areas.