Hide number of tor clients running on a shared network
For multiple machines/users behind a single network, each machine should run its own tor instance (more than one, in the case of TBB's), but this leaks metadata about the quantity and timing of tor usage to eavesdroppers/ISP's. For instance, each TBB instance will open a connection to its own guard on startup, so an eavesdropper can enumerate the number of different TBB users (for long-lived installs) and the times when they're most likely to be active.
Ideally, tor should provide a mechanism to obscure the number of different instances running on a network, either making them all look like a single client, or an indeterminite number of clients with random start/stop times.
To do this, at least the guards will need to be synchronized between tor instances (#15243 (moved)). Even with guards synchronized, each instance will open its own TCP connection to that guard; the TCP connections would either need to be multiplexed into a single connection, or split into a random number of independent-looking streams.