You've framed tenants as a liability rather than an important part of the housing ecosystem, combined with treating second/third/fourth homes as investment vehicles instead of alternatives. I sympathize with how eviction policy creates bad incentives on both sides, but I also recognize that this is largely also about supporting a healthy city of a blend of homeowners and renters.

While I think normalizing vacant properties is a worthy goal, I do think there's other ways of achieving this goal, such as other commenters have suggested around instead of an additional tax, reducing tax write-offs for vacancy, along with a better definition of what a vacancy is. For example your suggestion, the having your friend move in loophole for some non market exchange. This has the potential to subvert the principle of the referendum.