Since Thunderbolt is based on PCI Express, it appears that it is possible to connect to multiple hosts using the PCI express standard. However there may be additional software or hardware required to do such bridging of multiple hosts sharing multiple devices, whether this is true on Thunderbolt or not is not clear.
Things to look into are Non-transparent Bridging of PCI Express and subsequently Non-transparent Bridging of Thunderbolt.
PCI Express and therefore Thunderbolt are both peer to peer interfaces just like FireWire so thats a plus. However PCI express appears to have some host specific needs according to PCI Express Peer-to-Peer Interconnect from GE.
Its low latency, high bandwidth, widespread support and costeffective silicon have made PCI Express ubiquitous. It can however, be used for more than merely communicating between a host and a peripheral: it has many advantages as a peerto-peer communications technology. Enabling this, however, demands an understanding of how PCI Express works. This paper outlines the complexities that need to be understood and overcome – and describes a GE software product that delivers a solution that masks those complexities from developers.
As of now the only thing that Apple has defined for connecting two Macs via Thunderbolt is Target Disk mode running over it.