It will be bad for the landowners who don't actually use the land. Landowners who make their money either renting out the land to others who actually use it well, or who just leave it vacant for 10 years until the value spiked.

Those landowners are nothing but a drag. All the other landowners will have some more tax, but the more they invested in improving the land, the lower the taxes will proportionately be.

Not having any lots vacant is unlikely to be optimal overall.

An LVT won't prevent vacant lots. It will just make it unprofitable, where currently it can easily be profitable to leave a lot vacant.

If it is always and with certainty unprofitable, why would there be vacant lots?