Why would you? Tax is a very effective mechanism to control economy. And don't have to think on extremes even! Very wealthy people are buying condos there just because it's the best (passive) investment for their cash. If you increase tax for vacant property it will incentivize selling over time,or at least renting.. more offer with less cost.
In a macro economical sense Canada already profited from getting foreign $ invested in buying those properties anyway, time to make Vancouver livable.
