What I see as the 'hard to solve' problem isn't the contract. That's difficult but ultimately resolves to logic and proofs of logic.

The difficult to resolve problem is enforcing what the contract is trying to measure. It doesn't magically authenticate the state of the real world or objects within it. It can't do things like answer the question: "Did the occupant cause harm or ware beyond normal to a rented unit?" It's very good at enforcing things like regular and timely payment, but can't help resolve things such as "Did the land lord fix plumbing issues when notified?".

It also can't fix things like the biased nature of arbitration (is which relate to the above and in particular relate to the inherent disadvantage of both not knowing and finding it difficult to ascertain the state of the real world at any given time), or the cost involved with performing such observations. Nor can it handle bad actors on the side of renters, either by lack of training/documentation on how to properly use things or direct acts of malice.