The issue is that housing is a necessity, and the relationship isn’t an equal one. A landlord can usually absorb vacancy, repairs, or a bad investment decision; a renter can’t easily absorb losing their home or a sudden 20% rent increase.
Right, so let's pass laws (where not already in place) that prevent sudden eviction (e.g. nobody should be able to be evicted if they are a few days late or even a few weeks) and prevent sudden 20% rent increases.
No need to pass laws that prevent eviction for years. We can solve all these problems without causing other problems.
Additionally, if they are behind on rent, the deposit will not be enough to handle both.
Not sure that's obvious (is it done that way anywhere?), but it is an intriguing idea.
On the positive side it does decrease the inefficiency of places sitting empty while a tenant is found, which is good.
On the downside, it kind of goes back to being a sudden eviction, since the current tenant can't predict when a new one will be found, so whenever it happens they'll have a short-notice to move out.
Also, unfortunately there exist people who will take this time to destroy the place, making it un-rentable, to perpetuate staying there. Need to handle this edge case somehow.