Several such projects already exist. They aren't very active, though. I guess the problem lies in trust, or lack of thereof.
Basically, organizer needs to be really serious about it, and he needs to find some serious projects.
This can be done using smart property/colored coins. There is no need for a site as ownership can be securely identified by client software.
A web site could, perhaps, act as a directory, i.e. a place where people can find information on particular property/coins.