it's a closed research question now, the benefits don't outweigh the risks. And even the entry guards can tell if you are relaying or originating a given stream in most cases, after all they can count the number of extend cells you passed through them and Tor almost always uses three hops. Two extend cells means you are the originator. Nodes need to be able to see the number of extend cells to limit how long your path is, I believe Tor is network limited to 8 hop paths although 3 and very rarely 4 is the default behavior of the default client. Otherwise you could construct a circuit with 3,000 nodes on it and cost each Tor node a kb for every kb you send into the network, would be a big DOS weakness since having enough bandwidth to DOS the most sturdy node would then be enough to DOS the entire network. If you are shipping product out and run as a relay it is especially bad since they could get lucky and decide to put everyone who runs a relay in your area under surveillance, if you are the only one you could really stick out as a potential suspect. Plus it makes you vulnerable to down time correlations between the relay and the online presence. That section of the Wiki was written many years ago obviously since it claims Tor only has a few hundred nodes, today it has 3,000 nodes and has had thousands for several years.