It seems like a cute solution. But it's a bit unnecessary, and complicated.
Ie you probably would want to tax under-occupation as well. (Otherwise you just declare a bunch of apartments as a single unit, and have a single dude check in every once in awhile. They did that in Britain, because of different legal treatment of trespassing between empty and `occupied' buildings.) But how do you define under-occupation? Where do you draw the line?
Just use a land tax. It's simpler and harder to evade.
I really like this idea, except that "market value" is vague, and would require a bit of work to determine accurately. Maybe the best you could do would be to have a by-block square footage to value chart to be used for these purposes (and you would want a definitive source anyways, to prevent gaming the market value side).
This could also help quite a bit with the property owned in New York as a way to launder money[1].
1: http://www.npr.org/sections/money/2016/05/27/479717380/episo...