I don't think "smart property" or "smart assets" under our current
understanding and technological level can exist without third parties.
I don't understand exactly what you mean with a "third party". Obviously, there must be an "issuer" that has some form of control of the "property" that is represented. In my example of hosting contracts it would be the entity that is offering the "physical" access to the server in the datacenter via credentials (normally the hosting provider or a reseller). In the case of a car with an access code, it must be the entity that controls the access control system and can guarantee access to the owner of the access code.
So smart property tokens would have characteristics of an "IOU", like those traded on different platforms like Ethereum, Ripple, or NXT; or on the Bitcoin blockchain via Counterparty or OpenAssets (thanks @krishnaprmod for examples).
Maybe you are thinking of a "smart property without an (human) issuer" - here I agree that technology is far away from that. But "smart property with an issuer" would surely be useful, because they would enable "decentralized trading" of these assets and new forms of crowdfunding - I started this thread to see if there are already experiencies with that.
You may be correct in that I am taking a strict interpretation of blockchain,
but IMO, the purpose of the blockchain was to prevent governments, banks,
or any conceivable third party from having the ability to control or seize
something that is allegedly your "property" (with Bitcoin, it is the token itself).
IMO if physical property was tagged to a token that is within a blockchain
system, but I am able to take control of that property outside of the blockchain,
it was never actually secured or maintained the same way that the blockchain
was designed to do. Unless the property has a unique unalterable fingerprint
that is inherent to that property, like a unique and unchangeable radioactive
decay of certain elements within that property or something like that, the
tagging to the blockchain and its token is only superficial. For example, I
can seize your car with a tow truck, and place it into a car compactor and
then crush it. The blockchain in this way, did not preserve your right to
control your property in the same way Satoshi envisioned. You will still
control your token representative, but your property is destroyed.
But it doesn't really matter because if you are willing to accept there is a
human issuer/arbiter/police/and court system for this type of blockchain
registration system, then I am just ranting over nothing.